I like the answers you got here vs the answers from the CB.
And I agree with them, too. Get a nice light sling. Mesh...are they still selling/making Solarveil fabric? Those seemed terrific.
Although we haven't been to Orlando with DS (I've been there alone, along with other HOT places in the South, and hubby's lived in Singapore, so we're not unaware of the heat level), the summer after he arrived was sick-and-wrong hot, and I held or wore him *everywhere*. We didn't even own a stroller until he was 2. I find it wonderful, because baby is *right there*. You can feel if he suddenly gets way too hot, you know if he's sweating, you know if he suddenly gets pale (like with heatstroke). Baby is also right there for nursing purposes, which is how they, of course, hydrate. It's just very convenient.
DS sweat FAR worse in the carseat, b/c of the padding, than he ever sweat while being worn or carried.
So I'd get an Ergo with the infant insert, make sure we both had shirts that covered our torsos so there was no bare skin sweating on bare skin, pop on a sunhat and probably some nice light, loose, arm and leg covering clothing for baby, and go!