Lately there has been quite a bit of chatter on here about mobility-challenged folks. Not wheelchair-bound, but walking slow and not able to leap tall buildings in a single bound. Hell, I'm 60 myself, not in the best of shape anymore and for our trips we certainly factor in the walkability, although as long as we're not rushingrushingrushing, we can sanely traverse plenty of ground daily and get good exercise in as well. You know, the iPhone mobile app that logs the number of steps--if you ain't doing 10,000 a day, you ain't doing it!
So, just from my observances in three trips to Italy, I've found, in no particular order:
--take Pompei slow & easy. Assume you're going to turn an ankle and maybe you won't. And eschew the sandals, it's not 79 A.D. The place is worth the uneven surfaces for anyone, however.
--in Rome, the bus is your friend. Yes, it's crowded even in off-season, but just because someone tells you, 'ah, geez, you can walk from the Vatican to Piazza Navona' doesn't mean you should actually do it. If there for a few nights, get a weekly bus/Metro pass (and a laminated transit map) at Termini or any tabacchi shop for 24 Euro. Walk and ride, you'll still get your steps in.
--cobblestones in Florence. Bad for feet, bad for spinner suitcases, really bad for people that walk backwards, as I do/did while talking to my wife while ahead of her. Easy to trip and fall that way. Be careful so you don't walk into the Uffizi with a head wound.
--in Sicily, pick your spots. In Taormina, we stayed at Hotel Villa Schuler, which was only a short grade down from the main drag, Corso Umberto. Other hotels would require a system of pulleys to get me back and forth. Be smart & logistically-sane when booking.
Enjoy your planning!