There's only so much that can do. I have the silver windscreen things on my windows, foil, white paper. Close the windows and curtains when it starts getting warmer outside than inside. Keep my bedroom door open to encourage air from the cooler part of the house to flow. Maybe it makes a difference, it's hard to tell. All I know is, even with the door open, the moment I step from the hallway into my room, it goes from mild to hot and stuffy. I've tried putting the fan in the doorway facing into my room to help suck the cooler air in, it makes little difference. A spray bottle and fan blowing directly on me is the only way to keep cool. Then in the evening, if we're lucky, all windows open.

I have a second floor (3rd floor to the Americans) bedroom facing almost directly south.

Also I heard, I think it was on a documentary some years ago, it takes about 2 weeks for the body to fully adjust to big changes in temperature, and we rarely get two weeks of consistency, so we can never adapt. I'll have to go look up if this is true.