The ocean in the Mayan Riviera is NOT calm... there's also a travel alert for Cancun, Mexico from US, British gov't.
Anguilla in the British West Indies has beautiful, calm beaches, US$ & very friendly locals. Check directly w/ a resort.
Also, Marriott hotels are excellent, find an island that you want to visit & contact the Marriott property directly. The Marriott Palm Desert, in CA is totally accessible, if you like a desert climate.
I'd also contact Club Med (Caribbean clubs), Sandals (and if you like kids) Beaches.com to ascertain which ones are accessible in Jamaica or Caribbean. Contact the resorts directly, do not take the opinion of an 800 operator.
We were misinformed by the Peninsula operator that an accessible toilet seat was n/a in Bangkok, but when we checked in, I called housekeeping & they brought one over in a few minutes with rubber mats to make the floor around the toilet safe.
Four Seasons also are excellent, if you can afford it. BTW, if you're getting a lot of rooms, negotiate with their sales office for a better room rate.