Something I’ve done for many years is cover windows with aluminum foil. Of course you can’t do it with all your windows, but I always have some that don’t show to the front or anywhere important to see out, and have lots of hot sun shining through. This is really really helpful in bedrooms. It’s cheap and easy, just cover all the glass using masking tape on the seams and edges, and placing the shiny side out.
This blocks out soooo much heat. In the Fall just pull it all off and let the warmth you want in the winter back in. Barbara in Texas