The key really is to use at least a cover that is made of breathable absorbing material. Better yet; a combination of that for both cover and cushion itself. Now obviously the cushion can be a rather expensive route when not getting (full) coverage for that, but you can already do quite a lot with just the cover.
Problem is that the norm in this world is non-breathable, "easy to clean". Read; let's make it so that any fluids don't penetrate and can easily be wiped off". Nice and peachy when going down that route for incontinence needs (and even than one will want to add a layer for the sweating), but it's also a succes recepy for your body having no place for the sweat to go to. Yet when sitting down fulltime, the body tends to sweat more/more easily around your bumm and thighs. You will want the material beneath you to absord the sweat for you, yet also be breathable enough to dry out, not smell bad within no time, being washable etc.
Most "official" covers are expensive. As soon as anything is labeled as aid, medical etc. the price goes up. Yet it can be very very cheap to get yourself more than one cover if you buy the fabric you like that is breathable and absorbing and then make the cover yourself, have a crafty friend make it or even when paying a professional. Always have at least 2 covers! Accidents do happen like dropping a drink or finding yourself out in a monsoon like rain without an umbrella. Two allows you to alternate while one is drying out, being washed etc.
Now for some the Florida summer can be another thing. Some people sweat more than others and some folks will spent more time in the full blazing sun that others (which will also influence sweating etc.). No big issue either. Something as simple as a towel can do the trick. Yes indeed, the same one you would use drying off yourself after a shower. After all; very absorbing fabric.
You can also make it easier or more difficult on yourself with the choice of clothes. Wearing breathable 100% cotton stuff will give a very different result than wearing less breathable fabrics, even more so when combining that with tight fit. Again you will want the fabric to be breathable and somewhat absorbing to take the sweaty away from your body and into the clothes and/or cover.