You can very well plan it so that a complete renovation is not necessary
not completely... but still in such a way that you have to put up a few walls, install a new bathroom on the ground floor, have to convert the staircase in case of rental, etc...
For these costs, you could probably also install an elevator... with the advantage of not having strangers in your house and not having to live in 70m²...
Being reduced from a 130m² house that you have for yourself to a 70m² apartment and still having to live with the additional noise from above is not exactly an elegant solution in my opinion... especially not if I am already making compromises in advance with which I have to live for years without any necessity..
I'm not saying that you shouldn't think about barrier-free living! That is definitely an important topic, even if you are still young! wide passages, level-access shower, etc... but before I convert a single-family house into 2 small residential units, I would rather look for other/better solutions....