My car doesn’t have insulation either but the AC absolutely makes a difference. Maybe your AC unit isn’t working - 40 years is a long time for a unit, may need cleaning or recharging, or just replacing.
Come to think of it, the house I grew up in didn’t have insulation either, and we’d have died with window AC units in the summer.
I'm already in a state of holding off on turning on my furnace. Had frost on my windshield the other morning. The afternoons are still warm enough to heat up the house with the curtains open and it's glory sleeping at night with the windows open. I did have a hydronic space heater on for a little bit this morning, though.
Anything over +20 C is to god damn hot, at least when you're cold you can add more layers. There's only so much you can take off when you're overheating.