I would recommend two stops en route by train.. The first is the small city of Lucca in Italy, west of Florence. It has a lovely historic Roman walled inner village surrounded by a high wide tree lined wall that you can walk and bike on. The old inner village has numerous quaint restaurants ,cobblestone lanes and walkways and a great operatic concert on selected evenings in one of the churches. If you go there, try to stay in a hotel close/adjacent to the old village. My wife and I stayed in a small bed and breakfast hotel -Ai Cipressi, right next to the old village. Walking distance (15- 20 minutes) from the train station, good breakfast, clean tidy rooms, and the owners speak english. Laundry just down the street and good local restaurants with 5 - 10 minutes walk. They also have guest use bicycles.
Next would be to stay in Villefranche-Sur-Mer a small village right on the Mediterranean just east of Nice. Great little village right on the main line and local rail tracks, and a short walk up the hill to the bus. Lovely seafront walk, good restaurants and decent accommodation. Also easy train and bus access into Monaco, Nice or train to Cannes for a day trip. We stayed in a budget bed and breakfast hotel (Hotel De La Darse) overlooking the marina . Nothing fancy but the owner speaks English, nice breakfast on a terrace facing the sea. If you stay there ask for a sea view room. No elevators though, but only three floors high.Hope this helps. No car rentals required for either of these spots.
Bruce