The amount of exposure protection required is an intensely personal thing. Every one has a different tolerance for cold.
For ME, I use a .5MM full suit (1/2 MM) when the temps are above 73 degrees. I use a 3MM full suit when it drops below 74 degrees. YMMV. Each diver needs to figure out what protection is needed for what temps for themselves.
Based on the limitations of what you currently own, I would suggest the 3MM shorty if you have decent bouyancy control (so that you can avoid contacting things around you). I would recommend the 5MM full suit if you have a history of brushing against things or if you get chilled easily or if you sunburn easily, or if there are a lot of nasties in the water.
Yes, one of the reasons for my .5MM is that it is sunblock that will not wash off! The Florida sun can be brutal to fair skinned people that aren't protected.
Remember that if you use the 5MM full suit and it is "too warm" you can always open zippers and flush water to minimize the effect. If you get too cold, there are fewer immediate remedies. However, pay attention to how warm you get during the SI.
One other alternative to consider is renting a 3MM full suit from a local (FLA) dive shop.
Just my opinions, and only because you asked.
Wristshot