I would also vote for St. Barthlemy, but bring along extra euros. A lot of them. Its beautiful, but big time expensive. Be sure to rent a car when you are there; taxi fares are totally outrageous. St. Jean Beach is fabulous, as are several other wonderful beaches but you'll need to bring along your own portable beach umbrella and towels. If you decide to go this route, I would strongly suggest finding an AirBnB right now that fits your price range. Hotel prices are off the charts for January and February, and you won't find a traditional hotel of any type for under $500 a night. You should be able to secure a nice apartment near Gustavia or up towards St. Jean Beach for around $175 to $200 per night. Be sure parking is included with the price. There are also two clothing optional beaches on the southern coast of St. Barts which are also quite beautiful -- Gouverneur and Anse de Grande Saline. Here's hoping the seaweed hasn't affected them.