Naples is just over one hour on the train from Sorrento .Sorrento would be a great base for Pompeii, Amalfi, Ravello, Capri, Positano etc. (you can get trains, buses or boats to thse very easily). Or yes, you could go to Sicily. You could either fly to Catania or Palermo, Cefalu is very nice, just under 1 hour from Palermo. or get the boat train from Naples (about 4 hours to Messina, 5 hours to Taormina).