December Honeymoon

I am looking for recommendations for an adult-only resort in the Caribbean during mid-December. I have not taken many tropical vacations before so so not know exactly what my criteria are. Will be traveling from NY and am fairly open to different locations. We really just need somewhere with good weather to relax and do some water activities. Budget could allow for up to $800/night for 2 people and am looking for the nicest option within that budget. Thank you in advance for any suggestions!