The house in Germany we finally bought features an almost perfect solution: the master bedroom is alone on the top floor and the only other room on this floor,

The house in Germany we finally bought features an almost perfect solution: the master bedroom is alone on the top floor and the only other room on this floor, separated by a 2sqm corridor, is a large bathroom. So you actually have 2 doors available to separate sounds from the bathroom from the bedroom and still have the privacy of an ensuite-bathroom only for the owners (as none of our frequent guests would "by accident" get to our floor.