VENICE: use the vaporettos (water buses) for minimum stress on knees. I think it's all those bridges that kill my knees.
CT: MONTEROSSO can be navigated with a minimum of climbing. Use taxis or the local bus to get around. Much of the town is flat. Stay in one of the waterfront hotels. Use the local buses in the other towns, too. With a CT card they are free. In RIOMAGGIORE there is an elevator to the top of the town. It is possible to walk along an almost level path for about 1/2 mile to enjoy the same views available from the more rigorous paths in that area.
LEVANTO & LA SPEZIA: if you take a taxi to the waterfront or beach, walking there is level.
VENTIMIGLIA at the Italian/French border. The town is mostly flat, has a long promenade along the beach, and is small enough to walk all over. Some hotels have elevators.
VERONA: is mostly flat.
MILAN, PISA, LUCCA, PALERMO, TAORMINO: once in town, these places are flat or it is easy to stay to the flat parts.