Floor plan: Single-family house 5.60 x 15.80m Do you have any ideas?

[*]At the bottom, a shared room for building services and a toilet. "That’s not done" – so what. You won’t scare off a guest with this, it’s enough for urgent business when coming home, and otherwise you just go upstairs.
[*]Housekeeping in terms of "laundry" is better accommodated upstairs anyway.
[*]Now consider placing the straight staircase as a room divider in the middle of the house – I know this from a similarly narrow house of a friend – the effect is simply great!
[*]On one side of the staircase comes the kitchen and a dining table, which normally stands with its long side against the staircase (2 people...), on the other side of the staircase the living area adjoins.
[*]The staircase ends in an "office corridor" from which compact rooms are accessible: bedroom, bathroom, guest room, and a small room for washing machine etc.
[*]It would be great if you could build another full floor, then the bedroom with roof terrace would be one above that and the work area larger.
[*]With an attic with a low knee wall, the variant with the bedroom upstairs could also be designed.
[*]Think of acoustic elements with this type of construction – this radically open design needs some attention here.
[*]A garage next to the house potentially costs a lot of light – like in a terraced house.
[*]If you want to stay in the house for a long time, build the rooms so that you can later add an external elevator.

Make your profile visitable and/or tell something about yourself

Well then everything is clear: let it be his concern whether he can build something sufficient for someone there, and you just keep looking. You can find something better than such a tightly tied belt anywhere, if I may freely quote the Bremen Town Musicians

I find it a very charming house in terms of layout (possibly replan the open space to get a larger kitchen). In our city, there are plenty of houses that are 5.00m wide. And they are all very charming and beautiful inside. I even believe that I find smaller rooms (as long as they are still functional) somehow "nicer." I have never felt uncomfortable in any of the narrow houses. In larger ones, however, I have. Maybe you can bring some daylight into the ground floor through the roof (with a Solatube or something like that).

I do not find the bathroom small at all. Bath, shower, large sink. Everything there and still space to put things down and move around. I have never had a 9 sqm bathroom. I now have 7 and that is really sufficient to move comfortably and put everything down.

Search for Schwabenhaus FAME-E-104. It is 6m wide, but might have a few ideas for you.
I think moving the entrance on the garage side more towards the middle of the house has advantages for the room layout. I would also experiment with a double spiral staircase opposite it...
What wall thickness does the house have? With the limited width, it is very important to reduce that as much as possible.

Do you dare something radical? If yes, you can turn necessity into an absolute gem. It just has to fit your life as a couple. Here are a few thoughts:

[*]Below, a shared room for building services and a toilet. "People don't do that" - so what. You won't scare off a guest with it, it's enough for urgent needs when coming home, and otherwise you just go upstairs. [*]Housekeeping in terms of "laundry" is better accommodated upstairs anyway. [*]Now consider placing the straight staircase as a room divider in the middle of the house – I know this from a similarly narrow house of a friend – the effect is simply great! [*]On one side of the staircase comes the kitchen and a dining table, which normally stands with a long side against the staircase (2 people...), on the other side of the staircase the living area connects. [*]The staircase leads into an "office corridor" from which compact rooms are accessible: bedroom, bathroom, guest room, and a small room for washing machine etc. [*]It would be great if you could build another full floor, then the bedroom with a roof terrace would be one floor above and the work area larger. [*]With an attic with a low knee wall, the variant of a bedroom upstairs could also be designed. [*]Think of acoustic elements with this type of construction – this radically open design needs some attention here. [*]A garage next to the house potentially costs a lot of light – like in a terraced house. [*]If you want to stay in the house for a long time, build the rooms so that you can later attach an external elevator.