Tom, I know where you're coming from. It's hot and humid just like that here in Japan (the southeast of the Asian continent, right around the same latitude as Georgia). When it gets humid like that nothing dries out because you never stop sweating. Synthetics stink to high heaven and close-fitting merino wool retains that moisture and feels clammy and miserably hot. Merino wool is not popular here during the summer months unless you climb high, where it is not humid. Lower down I would recommend wearing a loose wool/ synthetic blend shirt which will dry somewhat and allow some ventilation. Nylon shirts and pants tend to be stiflingly hot because the air does not move about easily. ALL the women who hike whom I know here will carry two shirts because of the sweat and humidity. If you're going to stay at sea level and not go very high I would actually go against the common grain and recommend taking one cotton shirt which cools because it does not dry out. Seersucker shirts are great for this. Cotton also takes a long time to start stinking up.
I have a feeling few people on BPL have actually spent much time in really muggy conditions, in jungles, so the differences in what are needed are not well known.
I also agree with you about insects and stinging plants, which are much more prevalent in sub-tropical and tropical places. Here in Japan in the lower levels you get three kinds of mosquitoes, black flies, no-see-ums, huge horseflies, giant bald-faced hornets that nest in the ground and every year kill people, foot-long venom-fanged centipedes that crawl into your shoes and under any loose net, leeches that loop across the ground towards you (you don't want to deal with them!), ticks, fleas, even super-heated acid-shooting bombardier beetles that hurt like all heck if you happen to put your hand on one of them... So yes, having protection from insects is a good thing in these places, though in most cases I have been fine (Scotland was the place I thought I'd lose my mind from the midges!).