I’m in Scotland so not as badly affected as those down south but I sympathise.
I’ve seen mentioned in a couple of places that people are fixing those silver survival blankets, like rescue teams and athletes use, to the outside of their windows to reflect the heat and it works quite well. They’re pretty inexpensive, too, from £1 each.
Temps here have dropped suddenly this evening and I think there’s a storm brewing. I hope you’re all more comfortable soon.