that is nasty and been there done that
never really experienced that in Bali - as long as you are not out walking long distances, or spending long hours in markets.
If you plan your time, with some tours, some pool or beach time, a spa treatment or two, its not to bad. The shops and markets are open daily from 10am till 10pm, and most of the temples are inland and a bit cooler.
I am not very fit and last december I did Besakih which is a huge temple complex set on the side of a hill.
Got a motorcyle ride up to the temple, from the car park, walked around and up the 1000 steps, took it slowly, no real drama.
In recent years I was more drenched last Saturday night in Sydney, marching in Mardi Gras from Hyde Park to the Showgrounds.
Do not let the threat of humidity stop you from enjoying Bali, we tend to sit by the pool during the day and go out for dinner at night and do a bit of shopping.
The bar scene at night is very good, so PM me for some details when you start planing your trip, and feel free to ask me questions as I know the island very well, and can make it a memorable holiday