In the humid, blazing hot summer days of the Ozarks I feel ya on this inquiry! Hard!
I usually prefer to work in the morning/evening hours and leave the hottest parts of the day for a siesta or cool spring fed creek dip, but I have found a few things that I prefer in the hottest months..
Natural material clothing! Linen and hemp to be exact. On ebay or other thrifting sites you can buy these clothing items used/basically new at great prices. I do find the 100% hemp or linen items to be the best.
Linen has hollow fibers which means that it is light while also being strong. Linen is the strongest natural fiber so the clothing will last you a long time as well. Both of these fibers also dry really fast (after absorbing 30% of their weight in water without noticeable side effects) if you do get really sweaty. That's a must because, let's face it, we're basically drenched in these conditions with our natural AC we've got going on. I just find that the natural fibers feel great, breathe well and can't be beat! Oh and of course always wearing a sun hat, drinking cool mint/lemon balm/tulsi teas, eating cucumbers and sometimes a wet washcloth on neck or head.
Hope this helps.
forest gardening in the Ozarks on 18 acres. 2 high tunnels, 3 acres of young food forests, tiny cabin living. solar off grid. building a straw bale house this summer - come intern with us! established 2016.
I think you should look into linen clothes, they are especially good for hot summer days. No wonder back in the days they used to wear linen almost everywhere.
This might be not your taste, but something like This would be comfortable.