I agree with Ronrosa, how warm or cold you will be is a matter of your personal tolerance to temperatures. I would rather be a little too warm and open a zipper or flood the suit a bit to cool off, than too cold and no way to get warm other than to surface.
I dived Aruba this past August, was comfortable in a 3mm rental shorty for most of the diving, but during last dive of a 3 dive day which was a drift dive, toward the end I wished I had a full suit or at least a hood. With a shorty I like having a skin underneath for abrasion protection on my arms and legs. Also, be sure to bring along a tropical weight hood, beanie, cap or some other type of head coverage. Sometimes that is all the extra you need, it's typically small, light weight and you can stuff it in a pocket when not needed. I would rather have it and not need it, than not have it and wish I did.
You should consider the type of diving you will be doing. Deeper or shallower. Drift diving with little movement, you might get colder faster than a non drift dive where you must kick to move through the water. Day vs Night, the water will be a bit colder without sun to warm it, and no sun to warm you on surface if you get cold. Also consider the number of dives you will be doing per day and overall for the trip. It does seem that cold tends to build over time.
I am going to Bonaire shortly and will be bringing a 3/2 full suit, and a 3mm hood. If I am too warm I can always rent a 3mm shorty or just use my skin.
Happy diving