Cozumel, MX is another good option, or elsewhere along the Mexican Riviera.
Any of the Netherlands Antillies. Aruba if wanting a more Americanized island experience, Curacao if you want a more Dutch island experience, St. Maarten if you want a near-to-St. Bart's island experience, Bonaire if you want a more laid back island scuba diving experience, Saba if you want an island rainforest experience (3 different ecologies depending on elevation plus the planet's shortest commercial airstrip), St. Eustatius if you want a real get-away-from-it-all experience with a black sand beach.
No idea how well recovered the USVI are yet post-Maria but you might find some deals there revitalizing the travel industry. St. Croix Cane Bay are is our favorite of the USVI as scuba divers.
Belize if you want a reef, rainforest, and ruins destination but that's too much to do in that time period, but a good pick for rain forest and a few ruins in that time frame.
Jamaica if you go to an all-inclusive for just a few days.
Recommend you check CDC recommendations before you choose. Some places it's wise to start anti-malaria meds specific for this hemisphere 2 weeks before departing, among other things. It's better to be preventatively medicated before you go than seeking medical care at a foreign destination (some spooky stories) or after you return IMO whether it's tetanus, typhoid, malaria, etc. The Cayman Islands, the Dutch islands, and USVI are particularly attractive for the minimal immunization recommendations compared to many nearby foreign destinations.