Edit: I myself went without medically required cooling for 10 years. Tinfoil over the sun facing windows can help, as can wearing tshirts or bandannas wrung out with water and draped on the back of your neck, frozen water bottles, facing a fan out the window at night to blow the hot air out so cooler air gets pulled in through another window (if safe to do so). Use any sash windows to your advantage https://www.womanandhome.com/homes/homes-news/victorian-sash-window-hack-air-conditioning/
But it's hard on the nights that don't cool down.
Definitely get a portable aircon if you have to, they're expensive and suck but are better than nothing. Evaporative coolers are cheaper and still better than nothing but I found they broke easily and were not good in humid weather.
I'm pretty concerned though about predicted issues with the grid.