It's worth asking - how much walking can you do? That might influence which cities would be better to visit, skip, etc. For instance, Venice is really tough if you can't walk much - there aren't cabs. Florence is great if you can walk ~1 mile because it's a small historic center and things are close by, but if you can't walk much at all, taxis are more limited. Rome might be the in-between. It's larger and things are more spread out, but taxis everywhere and generally available.