Barrier-free accessibility in old age is quite a thing. There is a site called nullbariere.
Sockets high up, wide doors, no thresholds, no steps for example to the terrace, lift-slide door instead of a normal balcony door.
Thank you very much for your tip with the website - very interesting - and your hints! Above all, the concrete numbers make it easier to provide appropriate measures here.
The discussion on the topic of accessibility has led us to the conclusion that we do not want to plan for every eventuality. As far as possible, we will implement one thing or another, only provide for some things, or simply omit them altogether.
There will be an accessible toilet only on the ground floor, where shower, washbasin, and toilet are in one room that makes sense to us and can leave enough space. Should the issue ever become critical (hopefully never), the lower room would be converted into a bedroom with an exit to the outside and the bathroom would be right next door.
If you have any further input, I would be happy to hear it.