I feel like this question was made for me! Not a mom, but a babywearing educator. As previous posters have mentioned, many carriers have meshy linings that would be best for the heat of Florida, though some of these are difficult to get your hands on (especially Tulas) but they are great if you can snag them. Additional ideas would be a linen ring sling (something like classic linen from sakura bloom or wrapsody's ring sling) because they are light and small enough to throw in a diaper bag, but you need to a) really be comfortable using this type of carrier and b) have a baby who doesn't want to straighten their legs all the time. Additionally there are lightweight wraps by wrapsody specifically for warm weather baby wearing. Again, there's a learning curve to wearing but if you are comfortable with it it's a nice option.
No matter what, I would recommend having something like a spray bottle and a possibly previously frozen wash cloth in your dipe bag to put between wearer & baby or on the back of necks. It's true that babywearing is always warm. The advantage is, though, at least you are close enough to always be checking in so you know at once if baby is overheating.
As for other mesh carriers- I wouldnt' get a mesh ring sling as these are meant specifically for water and utilize buoyancy to keep safe.
Previous poster mentioned beco gemini - that's a GREAT carrier and even though it is foam based it has a narrow panel so more air flow between wearer and baby if that makes any sense. That being said if you don't already have one, you won't get a ton of use if you start at 9 months because baby will grow out (as in get too long, not unsafely heavy) pretty soon after that.
Mei Tais I love, esp in the heat, esp if you can find one with breathable weave in the fabric.
I feel like I just text assaulted this thread lol, but I'm happy to throw out answers to questions. Since I do not have babies myself, I can only give my opinions, not life experience, though I do wear my friend's kids when I'm babysitting
