Nakedness is key here. It’s been stated many times before, so I just wanted to hammer that home.
Ceiling fans are nice. Put these two together, and you’ve got a comfortable day.
Another thing I do for those really hot days is I keep a small towel in the freezer (hand towel size will do). Don’t get it wet or anything, you don’t want it covered with ice, just cold. When you feel you need it, take it out, and either lay it down under you, or put it on top of you, whichever you feel necessary.
I’ll throw in another vote for “air conditioning is civilization.” I grew up in Massachusetts and one of the many things I hated was that New England attitude of “Air conditioning? That’s not necessary here. It’s only hot for 2 weeks a year anyway.” No. It’s not. And even if that was the case (which it’s not, I might add) the expense of air conditioning would still be worth it! Heathens! Now I live in Florida where everything has central air and life is good. It’s not that I don’t like the heat, either - I’m not comfortable if it’s below 80 degrees outdoors and I tend to keep my house around 76. But there’s just no need for all that humidity and associated sweating. Really.
Basements are cooler. Civilized lands have basements that are inhabitable.