Small Bungalow Floor Plan - Optimization Potential?

Not me, but the OP is avoiding the utility room directly next to the bedroom.

True. That’s what I wanted to address. In a two-room house, of course some rooms have contact points or shared walls. Regarding the noise problem: ventilation system is not to be installed, heat pump, does the indoor unit make noise? I don’t know. We have silent gas. You can no longer hear our washing machine at all. There are mats for spin cycles. However, I wouldn’t let the floor plan be dictated because of 5 minutes a week – the dishwasher is probably more interesting in that regard. Be that as it may.

We have a washing machine in the adjacent bathroom, which is actually not a problem; moreover, as a single person you probably wash less often than a large family. We turn on the dishwasher before going to bed and I wouldn’t see that as a problem with today’s appliances either.
The nice thing about living alone is that you can do everything exactly the way you want and where/how it bothers you or not; that is very individual. Even our WW heat pump in the utility room next to the kitchen is not really disturbing when it switches on for a while.
Living in an open or, as here, "smaller" space also comes with such "disadvantages," which I do not perceive as such because I like my way of living. In the end, every decision for a detail always comes with some consequence, so I pay attention to my priorities.

You could thus tear apart any great floor plan of a house with references to extreme cooking odors, loud kitchen work or machines, lack of privacy when having visitors, etc., but in my opinion the above principle helps here; I live in "my" normality and not in a possible extreme case.

I admit, I have now had 3 attempts with about 70/75 sqm, but discarded them again. Planning a house is not easier when you only have 3 rectangles to zone (bedroom, bathroom, utility room)

I would also first look at how many sqm are actually needed to get a nice floor plan for me, rather than forcibly trying to stick to 75 sqm. If you do not waste unnecessary money in execution or really consistently avoid unnecessary cost drivers (which you are not wired that way), it should also work with the budget at 85 sqm.

trying to forcibly stick to the 75sqm.

No one here is forcibly adhering to strictly defined sizes. The OP initially was at 70sqm and allows for some flexibility.
But a bathroom of 8-10sqm as well as a utility room of 7-10sqm should be sufficient for a one- to two-person household. And if you know standard furniture dimensions, then everything fits wonderfully according to the wishes. However, if you approach this with castle-sized measurements, you are doing something wrong.

but in my opinion the above principle helps here; I live in "my" normality and not in the possible extreme case.

That's right.

nobody here sticks rigidly to fixed sizes by force. The OP started with 70sqm and leaves room for increase.

I already understood that, it was rather meant for the OP to come to terms with "necessarily" more sqm.

But a bathroom of 8-10sqm as well as a utility room of 7-10sqm should be sufficient for a one- to two-person household.

We have our bathroom on the ground floor with 6.91sqm and I was skeptical during planning. Now I would do it the same way again, it has become "my" bathroom, just like our utility/technical room including photovoltaics and a hot water heat pump. Despite an additional garden exit and hand washbasin, there is still enough shelf space next to the technology. Of course, bigger is always better but for us this is absolutely enough; rather, we would declutter again if needed. I can’t draw floor plans, more likely to "nag" about them, but we have exactly 90sqm in the rectangular ground floor with the entrance on the long eaves side for utility room, bathroom, open corridor (7sqm) and large all-purpose room as well as a staircase (which the OP doesn’t have), so it is clear to me that even with 5-10sqm less for the OP it can be a super spacious feeling thing if it is kept open and bright (windows).

Of course bigger is always better

I don’t agree with that at all, for example. With regard to the bathroom, having too much space can make planning very uncomfortable. The sofa area also gains atmosphere when there are walls around it. However, if it’s too small, it restricts the activity area in front of the TV. Some don’t need anything there, but many want to do some exercise or whatever in front of it.. (we still have that Nintendo Wii thing in the drawer. Hehe You don’t have to overdo it and put the same lid on everyone. You often see this with granny flats, which, despite much criticism, many forums think should ideally have 120 sqm. Hehe, a small apartment works if it is well planned. What the corridor on the eaves side is on a rectangular floor plan, the door to a room is: if set incorrectly, it can mean needing more sqm to get the same comfort.

I don't agree with that at all, for example. Regarding the bathroom, having too much space can make the planning very uncomfortable.

That's correct, or rather I expressed myself inaccurately. I was actually thinking more of the utility room, where space can sometimes be tight. But even there, it's important to exercise discipline. Often, bathrooms are unnecessarily and without deeper reason too large; as I mentioned, I love my 6.91 sqm bathroom.