I also second Nike DriFit. As far as decreasing body temperature, it is better to go one layer. The thicker the fabric you wear, the hotter you are likely to be. More fabric also means more fabric to be soaked by sweat, and a longer to dry. The object of a moisture wicking shirt is to absorb the sweat from the body, transport the sweat from one side of the fabric to the atmosphere to allow your sweat to evaporate ( 1 KJ of heat is loss per L of evaporated sweat). Wearing baggy shirts only helps if the temperature outside is cooler than body temperature. When you walk you create air circulation in the baggy parts of the shirt (convection) and you loose heat as the motion moves air away from the hot body to cooler atmosphere. In Florida, the temperature will be high, so only hot air will be recycled. It is so humid in Florida, there is literally no where for your sweat to evaporate in the air. Think when its 100% humidity, no more moisture can be added to the air. I recommend Dri Fit, because it doesn't hold on to as much moisture, and in the event that it is not as humid, you will feel drier unlike a cotton shirt which holds onto more moisture than other fabrics.
- Sorry for the lecture.