Thermal comfort is somewhat idiosyncratic.
To put it in perspective, below is a piece from my June '00 "Ask RSD" column in "Rodale's Scuba Diving":
"Have you ever been out on the street in the spring or fall and noticed people wearing everything from shorts & T-shirts to full coats with hats & scarves, all apparently in comfort? Well, things are no different underwater. This comfort is highly variable among individuals depending on such factors as percentage of body fat, age & tolerance to thermal discomfort. Other determinants, like how many dives a day over how many days you are planning, are also important. When you ask "What wetsuit should I wear?, you'll get answers ranging all the way from "just a bathing suit" through "5 mm full."
The question is better asked: "What water temps can I anticipate at my destination?" You'll receive a pretty accurate answer to this, and then can decide what's best for you based on your personal thermal comfort needs.
It's always a good idea to come thermally prepared, just in case."
That having been said, in late Dec in Nassau you'll be looking at surface water temps of ~78 plus/minus a degree. Scuba temps will be more like 76 plus/minus a degree.
Personally, a skin wouldn't keep me warm. I'd take my 3mm full & beanie, at the least.
Have a good time.
DocVikingo