I have an AC, but it only does so much. Most of the summer, it's been above 80F indoors. I'm also kind of menopause-y due to low estrogen, and I have hyperhidrosis, so I've just been miserable.
A dehumidifier is a huge help. "Dry heat" makes a difference - 90F in Arizona is pleasant and comfy, but 70F in Iowa could have you dripping wet because of the humidity. Also, fans, so many fans. Vortex fans are the most powerful and effective at cooling. A floor fan that you can stand over and hold your shirt or dress over so the air blows up your body feels incredible. And don't underestimate the classic hand fan, I find that cooling my face is more effective than cooling my body at making myself feel like I'm not dying.
Avoiding synthetic fabrics has been a HUGE help, but it can be difficult, as almost everything is polyester now. I've tested it so many times, and I'm noticeably hotter in a poly/cotton blend than in a pure cotton, even if the pure cotton is a thicker fabric. Polyester, polyamide, and nylon are thermoplastic fibers, and they trap heat against your body, making you hotter. They're often good at wicking moisture, which is why they're used in workout gear, but they keep your heat in. Rayon, of all the synthetic fibers, is at least a cellulose fiber instead of plastic, so it won't do that. Like cotton, it's pretty breathable, but not super at moisture wicking. Linen is the superior hot weather fiber, if you can find clothes made from it. It's breathable, it's moisture wicking, and it keeps cold air next to your body. It's why you'll see people wearing historical clothes and not melting from the heat despite multiple layers, while people in modern polyester garments are withering. Loose clothing will let cool air flow around your body better than snug clothing, so I ditch the leggings for a caftan and swan around the house like I'm an old-timey movie star.
I also straight up ice myself. Placing ice packs in areas where the blood flows closer to the skin's surface is standard treatment for heat stroke, and will prevent it if you're on the way: back of the neck, armpits, and groin. I lay in bed covered in ice packs until they're warm.
Cold showers can also help, but I'm the kind of people who can break out in a sweat from the energy expenditure even in a cold shower, so it's not for everyone.
Strategic use of window opening + closing is big. Check the hourly forecast, and note when the coldest & hottest parts of the day are. Open the windows as it's getting colder. When it starts to heat back up, close the windows, as well as the blinds/curtains on the side of the house facing the sun. For me, the coldest part of the day is right around sunrise, so 5-6am in the peak of summer, and the hottest part is around 6-7pm, before the sun starts to set. Typically, I will open the windows around 8-9pm, and let the cooling air come in. I try to close them, and the blinds, by 7am, so I can trap all the cold air inside. Blackout curtains, or a blanket over the window, will make this effect more extreme.
I also try to not move more than necessary, and not eat anything that requires heat. Lots of peanut butter and jelly, washed down with ice water. I cut out caffeine, since it's a diuretic, and drink lots of Gatorade to replace all the electrolytes I'm sweating out. Cleaning is done after the sun goes down, and if I have to use the stove, I'll open the kitchen door to help get the hot air out. I keep the lights out during the day, too, because those generate more heat that I don't want.