I see you are from Rhode Island--I'm originally from CT, and also a fan of doing nothing on vacation, and understand the need to go somewhere warm in winter from new England, so I think I have an idea of what you are looking for. I am a fan of Sint Maarten--there is a water taxi, something like $5 or $6 for the day unlimited back and forth, that takes you across Great Bay and docks you right by the beach. Some may not like this beach because it is not exotic, tropical, isolated...but it is convenient, the water is warm and mostly clear (sometimes gets stirred up by a wave runner nearby or something like that), the sand is not rocky, and for a few dollars you can get set up on a comfortable lounge and have drink service at one of many stops along the beach. Easy return access to the ship, which is always in sight.
St. Thomas does require you to at least hop a taxi to get to a beach, but there are several, they are much prettier, and it is EASY to find the cab (really an open air truck w/ a few rows of benches) right off the ship and from the major beaches there are plenty of return taxis, or tell your driver what time you want to return. We did Magen's Bay last time on the Eastern, there are no waves, crystal clear water smooth clean sand--you might yourself saying "Toto, we're not in Narragansett anymore". We stayed until 1 or 2. Bit of a lengthy ride, but scenic as it climbed over the highest hills of the island to get to the beach. Others will recommend other beaches.
Great recommendation above that the spas have lots of availability during port days. And the pools are open and not terribly crowded.
Castaway Cay is heaven. Though I am not a fan of their ribs, but I get spoiled living in the south now.
