At that time of year Amboise too would be dreary and void of tourists who liven up the place -I'd suggest maybe staying in south of France or Avignon area for somewhat better weather or better yet going to Paris for an extra two nights - maybe do a day trip to say Reims or Chartres, etc.

Yes to Sorrento as a utilitarian base for Naples, Pompeii, Capri and a day trip to say Positano or Amalfi itself.