I would do the same upstairs. Also pay attention to a spacious master bedroom for seniors. So that a 2x2 meter bed fits in and there is still room for a walker, etc. (2x2 m so that one side can accommodate a hospital bed). Seniors (young people are rarely affected) find it difficult to move again, even if it is only within the house. I don't know why. It was important to my father that as little as possible changed, and the father of a friend refuses to move out even though it really makes sense.
Much of it is comfort and not necessarily associated with additional costs, e.g. wide doors, high sockets. Some things must be considered in the floor plan — if necessary, it requires a bit more Tetris from you. Google "Nullbariere." There you will find turning circles, clearance areas, arrangements, etc. We have also taken this into account. So far, no expert has commented on it. So no hospital or nursing home look. Make sure that in any extensions to the WC, reinforcements are installed so that grab bars can be attached. In our case, a wooden beam was simply installed. Floor-level shower — this is almost state of the art.
Important: no matter what you build, always draw existing or desired furniture to scale repeatedly. Consider traffic routes, open cupboard doors, occupied chairs.