My dermatologist recommended a powder called “Anti-Monkey Butt” powder. I use it under the breasts, and creases of my legs, the inside of my thighs, etc. It really helps keep me dryer and eliminates chafing.
I use summer's eve anti chafing gel and it works pretty well. I have a thyroid problem too even though mine is under control because of meds. Hope this helps
It would seem that wearing something more absorbent, looser, or a fabric designed to be wicking of the sweat is the way to handle sweat per se. If the problem is that you want to sweat less primarily because the sweat burns, then I'd talk to your doctor about adusting your thyroid medications, or talk to a dermatologist to see if there is any topical cream that can be put on the skin.