Get sun shades for the ceiling. It will help keep the heat down. I just got the Tesla ones (not cheap), but they really seem to help. Lots of Youtube vids about that. The Tesla ones cover the entire back window. Also get a front windshield screen. Those are the silvery-bubbled ones. They do an amazing job at reflecting heat.
If your windows are tinted with UV tint, that will also help. Happy sailing.