Ooooooh...that's a bit tricky. It is hard to find good high boots that are lightweight. With the military surplus ones, you may find that they tear up your tootsies. My uncle's Viet Nam issue boots rubbed his feet raw
. Then again they might be quite comfortable. A lot depends on how old they are and from what country's military.
The problem you will face with waterproof boots in a hot, humid environment is that your feet will sweat buckets and you can end up with a bad case of athlete's foot. That happened to me last summer, and my 3 season boots are mid-cut Timberland Mt. Maddsen Earthkeeper's...and yes, they are waterproof.