My fiance and I will be in Bonaire and Curacao for our honeymoon in 3 weeks and have never been to the carribean. She is a very cold natured person and will be wearing a 5mm hyperstretch suit.
Not only will she be too warm in 5mm, but quite bouyant, which means she will need a lot of weight. Trust me, this is NOT a good combination.
I too get cold quickly, but find that a full 3mm is just fine. However, I also have an Aeroskin sleevless vest that I can wear under the suit to add another layer to my core. They are especially good because they don't add any buoyancy.
~SubMariner~