What wattage bulb should i use?

I have a BP and an adult female leo and im thinking about getting another leo for xmas. Male or female im not sure yet but ill probably get a male so i could breed in a few years...

but my question is, since i dont really want to buy a separate thermostat just for QT,what wattage infured bulb could i use 24/7 to get my temps to 88-90 daytime and 70+ nighttime for an adult leo? My temps get pretty cold around 50F in my house(thats just an estimate since its 40F at 7 in the morning outside) at night, and probably 60-70F daytime. So what wattage infared bulb shuold i use to heat the basking spot/warm side to 88-90 daytime temp?