Another option is Grand Cayman - but it's pricey there. Not much in the way of taxes since the offshore banking takes care of that but I once read about the residency permit requirements - apparently you put 500K into property/a business venture and you get a 25 year permit renewable indefinitely. IDK how that works on a straight retirement basis.
One thing they've got happening now is there's this new state of the art Medical City complex - a large Indian medical group has a specialty clinc there now near the Breakers on the south side. And Cayman seems to be going after medical tourism - there was a movement recently to add jetways to the airport to handle the anticipated wheelchair traffic.
My sister was just there looking at property, they couldn't find much decent in a condo for under $400K. They bought a tourist condo (weekly rental) on the Brac for 1/2 that. 30 min. flight to GC for most things and the weekly barge brings everything else.
The Cayman Islands recently (either in 2015 or 2014) toughened up their already strict immigration requirements. In order to establish permanent residency you need to show an income of at least $120k CI annually (without being allowed to work there) and make an investment in $500k in the country ($250k in residential real estate).
Residency Certificate for Persons of Independent Means
If Grand Cayman is your ultimate destination you may have better luck establishing residency and earning citizenship in a Caricom country and then relocating.