Floor plan of a 200m2 house, your assessment?

We would have a great view on the top floor, hence the consideration to build three stories.

I think it was a mistake to post the exterior view because it is misleading. This is just ONE design of how it could look.

Maybe you should reconsider your priorities great view / accessibility first.
"A great view" is nice. But you don't spend the whole day in front of the window. And if you did, you would have to consider if you can still get up there... or for how long. As I understand it, you would also have a nice view on the living floor?! Are you mostly out with the dogs?

Would you have any further comments on accessibility or possible problems? Thanks!

The problem is the situation at age 58: I assume that accessibility is planned only preventively?
At 58 you are still in the middle of life, actively working (and probably still at 70). This means nowadays that you can probably use your stairs actively and fit for another 20 years (excluding accidents and gradual/sudden illnesses, which can also affect a 30-year-old). However, experience and our predecessors' lives show that from about age 50 (or so, plus or minus), the building of a house should somewhat include the last phase of life.
Many people realize this with a bungalow, others buy a hillside plot because of the great view... the latter is quite unreasonable, but of course also finally a dream project fulfilled for their own life – apparently your first house. You can tell by the whole wishlist that won't fit into the budget (we won't dwell on that further now).

Still, the budget will be the lever for you to be clear about what you want and what you can/must do without!
Building a house is usually no wish concert, and one has to humbly subordinate to the budget or make compromises for other reasons, e.g. with a hillside.
I myself am also with my husband at the same age as a "mixed calculation." When we built, we were 9 years younger. From a planned bungalow for two people, it became two levels – exactly because I want to live fully in the house and a bungalow would have been too small. We are not old grannies satisfied with two hospital beds. I am always a bit shocked how some builders with children’s wishes (a younger age group) plan a granny flat that is like a "basic hole."
I have standards, and my husband's bathroom doesn't (yet) need a bathtub grip. Also, with his regularly swelling feet, he will rather creep up and down the stairs than have a lift installed. And if bedriddenness really comes, then possibly temporarily in the office; in the long run, neither of us will expect care from the other. With a wheelchair, you also won't be cleaning windows or running around the levels to clean... so the cards will be reshuffled.

especially in your late 50s without children you really don't need >200sqm on 3 levels, do you?

Does every child need their own room? In short: you build what you can and want. A house should bring comfort, and everyone decides that for themselves. However, opinions and demands also change. Therefore, I wouldn't judge that as an outsider.
I could easily live in 200 sqm with my hobbies and husband, so could the OP . But I wonder if a 45 sqm mobile home wouldn't also bring me joy ;)

2 floors would be the plan B in case it is necessary for budget reasons. At the moment, however, we want to pursue plan A.

I quote myself:

Maybe you should reconsider your priorities great view/accessibility.

Budget-wise that could mean: everything a bit smaller and simpler equipment. Lines of sight are also there to simulate some size where it doesn’t exist.
Ask yourself whether such a panoramic thing up there will even be used, just like a built-in sauna.
I would basically mix the rooms. I have to say, the height dimensions are not so different that you absolutely have to build three levels?

But the basement is still completely unbalanced for me, but unfortunately I have no concrete idea how it could be better. I would also be very grateful for suggestions there.

since you apparently have a good architect at hand,

Is there really an architect involved?

Would you have an idea regarding the WC? Would you leave the door as proposed?

New thought, new design... and also consider a bit more privacy.

Quickly sketched (without knowing the house design dimensions): 154 sqm including roof terrace, 2 floors, living room without terrace access due to the slope... 450,000 €, + earthworks slope 50,000 €, + special equipment like sauna, fireplace 50,000 € + buffer

die Bodenbeläge aus dem Outlet etc. kauft?

Gussasphalt-Estrich just isn't available in the outlet ;)

1) Do you really want a room of >80sqm that serves for everything? Have you ever stood in such a room? … I would therefore definitely start with the question of whether the floor area can be reduced towards 160sqm? 2) In my opinion, you should openly discuss with the architect whether the rooms and floor area can be arranged in such a way that you remain with 2 levels. I have in mind the layout of a very specific house from England. 3) May I ask to what extent you are prepared for this? Is it initially only about the impression of the room and the kitchen may come from IKEA, the sanitary fixtures cheaply from the hardware store, … 4) … The WCs are each small chambers in which I would not feel comfortable even in my early 30s. … The doors must be 1m wide, the showers generous, enough space for maneuvering within the bathroom.

First of all, many thanks for your thoughts and your kind introduction. Regarding your remarks: 1. I fully agree that the size might be reduced without major losses. I am just trying to get an idea of the "how"... Currently, we live with an open living/dining/kitchen area of about 65 sqm. So the size is not unfamiliar to me. And since it is not 5m but only 2.60m, there is no echo either. We had planned between 2.80 and 3m. In any case, we would like to preserve this openness and spaciousness in the living area. 2. This house interests me very much and I would be happy if you find a way to write me more about it. 3. Exactly – primarily it is about a thoughtful, functional, and creative planning of the room. Regarding materials and interior design, we are very flexible. It’s not about brands but quality products. And we have no problem with an IKEA kitchen combined with fine dishes or an industrial floor with a great rug, etc. 4. Obviously, the area in the living area is more important to us than in the toilets… ;) But I have heard the many hints and see that we need to think differently here if accessibility is important to us. Thanks again and the reference to the house would be very welcome.

I agree, but I would also plan the space and ceiling breakthrough preparation for a so-called home lift. Something like that can also be retrofitted later.

That would also be one of our considerations. But another architect told me that it doesn't make much sense because (at least with 3 floors) you have all the costs for the shaft etc. and basically only save on the lift itself.

Such a building must never suffer from a lack of budget, because then the whole flair of such a project is destroyed.

Here you don’t want cheap parquet, no white plastic windows, no standard kitchen or lamps from the hardware store.
…

There are great low-budget projects in this style. But they also have to be lived through and through!

Thanks :)

That’s the point. The examples you list, we definitely don’t want. Although – we do have one lamp from the hardware store already. Self-made from installation pipes and connectors and with colorful cables from IKEA and simple light bulbs. Visitors find it quite successful. ;)

If you had a few examples of creative low-budget projects for me, I would be very grateful.

Barrier-free living in old age is quite a thing. Where does it pinch? To what extent does a couple continue living in the house? Because of the elevator, I guess with you up to the point where nursing care is no longer possible.

There is a website called nullbariere. There you will find information about turning circles, space requirements, etc.
Doors with 100 cm width are good to pass through with a wheelchair or walker without sore ankles. It also does not yet look like a hospital.
Imagine it simply no longer works and you are pushing a walker, walking backwards becomes difficult, the nursing service helps with personal hygiene, bending down is hard, every threshold becomes a tripping hazard. Many still relatively fit seniors have one or another problem.
Sockets high up, wide doors, no thresholds, no steps e.g. to the terrace, lift and slide door instead of a normal balcony door.