On a budget:
Cocoa Beach, Florida, all Marriott properties are very good! Plenty of wonderful places to enjoy!
Honolulu or Maui, wonderful experiences you will enjoy at either place.
Be careful about some places that are NOT SAFE today. Pick a place that is comfortable for you! Have a Marriott help you with travel arrangements!
Sounds like a good plan. Here's where my wife and I have booked five nights in late September (East Coast):
However, our all-time favorite beach for relaxing, walking on beach, dining (in and out of hotel) is Myrtle Beach, and if you're Marriott Vacation Club members, there are five high-rise villas (such as two shown below) also available at the site, across from Marriott Hotel & Resort:
For West Coast you might consider Newport Beach, CA:
If you prefer off shore, try Frenchman's Cove - Marriott's Frenchman's Cove: St. Thomas Resorts and Timeshare Rentals
Also in the Caribbean, one of my favorites is the Ocean Club on Paradise Island; however, it is not a Marriott property. You might recognize that some of the first scenes from the James Bond Movie, "Casino Royale", were filmed here. There's a mile private beach, and only some 50 rooms :
Hope this is helpful !