In reply to Trangia:
We had three nights there last year, plus 2 nights in Sorento and two in Naples.
Thoroughly enjoyed and the bus network worked very well for us.
I think we used the Cicerone guide.
We also enjoyed the walking on the mainland, though found Sorrento a bit too touristy, but a good base for public transport.
Iirc the bus company has a good app.
In the Lakes at the moment, but will try and get more information if you want on my return.
I do recall that in the shoulder season less ferries run, ie ishica to Sorrento, but ishica to naples is well served as people commute to work on those services.