Italy, Sorrento, and all things Amalfi in December and January

We just visited that area (beginning of November). If you want to visit Pompeii and the Amalfi cities, Sorrento is a good base. We enjoyed our time in Pompeii and did it on the way from Rome to Sorrento. We traveled via the Circumvesiana train between Naples, Pompeii and Sorrento. In Sorrento we stayed at a very reasonable BnB just off the town square, La Magnolia. It was pleasant, super clean and had a nice breakfast. The bus between the cities worked quite well, though be aware that it takes about 1 1/2 hours to get from Sorrento to Amalfi. We really enjoyed Ravella which is a short bus ride from Amalfi. If you plan to visit a couple of the cities in one day the day pass is convenient and offers a slight savings. We had more rain than we would have liked, but made do. I would be prepared for that possibility. For the most part, I used the RS Italy guide. I also used some RS walking tours, both from the book and from the app.

EDITED TO ADD: While we were there, the city of Sorrento was putting up lots of Christmas decorations, including a large Xmas tree in the town square. Not sure how long they keep it up but it should look pretty spectacular.

You will get more replies if you post this in the Italy Forum, here: https://community.ricksteves.com/travel-forum/italy.

This section, where you posted, is for post-trip reviews,

Mary, ferries will not be running along most of the coast in January. Weather permitting, you would be able to access Sorrento from Naples by ferry, and Capri via Sorrento or Naples but that's about it. The boats do not service Amalfi or Positano in winter so you'd need to use the SITA buses to access those towns.

Sorrento is a good base as it will have more open during the off season than Positano or Amalfi. There's some love on this forum for Salerno as well.

Travel info for Sorrento:
https://www.sorrentoinsider.com

For Capri:
https://www.capri.net

For Salerno (I think this is the right site):
https://www.livesalerno.com

Ferries (use dropdown to change departure/arrival locations):
https://www.sorrentoinsider.com/en/ferry-schedule

Understand that weather is a crapshoot in winter. You could get reasonably balmy and sunny, or windy, chilly and pouring rain. There are few indoor attractions on the A.C. so being willing to deal with the elements is a consideration. You could also take a train into Naples for the excellent archeological museum, (https://www.museoarcheologiconapoli.it/en/) some churches and whatnot if Mother Nature isn't cooperating.

Pompeii is, of course, a huge tourist magnet in this region and for good reason: It's easily reached from Naples or Sorrento via cheap Circumvesuviana commuter train, or trains between Naples and Salerno, although you'd use different entrances depending on which city you'd be accessing it from. Herculaneum is another excellent site to explore if interested in ancient Vesuvian casualties.

http://pompeiisites.org/en/
https://www.visitpompeiivesuvius.com/en/herculaneum

Note that exploring both sites involves spending most of your time outside.

At this point, restaurants are probably the least of your concerns: first figure out where to stay, how LONG to stay and what to sightsee based on what the tourism sites provide for ideas. You do not need guided tours for anything, although a guide for Pompeii can be useful if otherwise not up to doing the prior research/self touring. Guides can be hired at the entrance, and this RS-partnered tour has seen great reviews as well:

https://www.sharedtours.com

An alternative to a guide for Pompeii would be the RS walking tour on the RS app. I thought it was pretty good, but was happy I'd done some reading because RS doesn't cover some areas I found really interesting. We used the walking tours/info in the RS guide for the Amalfi cities and Sorrento. The Amalfi church was particularly interesting.

We didn't get as far as Salerno, but depending on how long you are planning for your trip, you might consider Paestum. I wished that we had the time for it.

Thanks for the all the info everyone!