Floor plan design single-family house approx. 160 sqm

Don’t you know that? Are we possibly special cases? I would definitely plan an additional toilet in the bathroom.

You are certainly not a special case. When brushing teeth, during the bathing session... you don’t want to go into the hallway and open two doors. One should also not build up too much prudery within the family. When teenagers get a bit awkward... okay... but you don’t build for that specifically. Toilet rituals that require some privacy can often be (well) planned into everyday life, and for that you would then also have a throne for yourself on the ground floor.

We definitely want an extra WC and it is right next door here. In our current apartment, we have to go across the entire apartment once and have not seen that as a problem so far.

Then you can use the downstairs WC
Keep in mind that you are not building for your bad habits. You can change those.
And keep in mind that children are different.

We have relapsed, and that already after the first day! [...]
We still don’t find the bedroom optimal, we’re currently figuring out how to get the bed to the other side so that we don’t have a window behind our heads.

This is exactly the typical course of Morbus StanSch:
1) just one last cigarette, just this one floor plan
2) that looks great, we’ve made some progress in it
3) but one tiny bit is still not right
4) 1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3, ...

Turn off the engine immediately,
otherwise cylinder head damage ! ! !