I love our 3 storey mid terrace, been here nearly 13 years, has been a very flexible space. Bought it as a new build when I got divorced, it was the cheapest way I could get a reasonable house with enough space for me and 2 DS.
Top floor is 3 beds and bathroom. Middle floor is living room and 4th bedroom with en suite. Ground floor is kitchen/diner, downstairs toilet and integral garage.
My 2 DS, now teens, one at uni, have always had top floor bedrooms. I did also have a top floor bedroom while they were growing up. Middle floor en suite bedroom was used as a separate reception room/teens study/playroom. The en suite shower was available for everyone to use.
Before DS1 was going to uni, we had a big bedroom swap. Me and (second time around) DH moved from our top floor bedroom to the middle floor en suite. Our old top floor bedroom has become our shared office for WFH.
DS1 and DS2 also swapped bedrooms to give DS2 the bigger one. Now they share the top floor bathroom. I love having our own private en suite.
We've got used to having a middle floor living room, it has advantages, it stays really warm in the winter. We've also decorated it very thoughtfully and bought furniture to fit the layout. It has French doors with a juliet balcony and a view over the garden, so has a lot of light and feels quite open.
DH and I only really go to the top floor now during the week for work as we both mainly WFH, so it gives us some separation between work and home. And it is much quieter being away from the DS bedrooms in the evening as they often stay up later than us.
We will probably stay here for a long time as we like the house and the area. DH hoovers the stairs, not my favourite job, but having 2 banisters is great for hanging sheets and duvets covers to dry in the winter.
And if we can't manage the stairs when we get really old, that would be an issue whether we had 2 or 3 stories, so we'd probably need a bungalow or flat anyway. But we could easily just live in the bottom 2 floors, with space on the top floor for DS when they visit.
We could have moved and upgraded when DH sold his house and we started living together. But we decided to stay here and pay off the mortgage instead. And we like the house so saw no reason to move.