I initially had the opposite problem where my uninsulated cinder block basement was too hot in the summer and too cold in the winter and my basement didn’t have any HVAC registers or returns. The only air conditioning it got was from a window AC unit and leakage from the HVAC ducts. Over several years I ended up adding 2" foam insulation internally to all the exterior walls, insulating the ceiling to the basement (mostly for sound absorption but it also helped with floor temperatures), and adding returns and registers in the basement. I also added an inline booster fan to help pull air up to a second floor bonus room that was an addition. Now the basement is always comfortable, the second floor is much more comfortable, and the energy costs are about the same. My moisture levels are 30-50% in the summer.