Hotter inside than outside must be a nightmare especially to sleep.
I manage to keep temperature around 23/24 during summer and exceptionality 26/27 during heat wave. But I don’t have AC.
It’s a bit more difficult on winter when the max temperature of the day is 1-2 degrees and there is no sun. Radiators need work frequently to keep 18 degrees.
I wish we would have more sunny winter days.
Traditional houses from the 70s are usually a basement and the house upstairs.
Basement is often half or totally underground.
Then the wall are made with cinder blocks, empty air and bricks.
There is chimney (not sure the term in English), so you can heat with wood, but most of the time there is central heating with Gaz or Fuel to replace or in complement.
How is it in your country ?