how do you keep your baby warm at night???

I live in Phoenix Arizona, and although this is a desert it can get cold (for us) at night. Last night his nursery dropped below 70 degrees. He wears footie pjs to bed and I try to make sure they are the little bit thicker material. However when he gets up in the middle of the night or early morning I can feel how cold his toes are through his footie pjs. I'm worried about making it too warm (SIDS), so turning on the heater worries me, but I also don't want it to be too cold... anyone else have this problem?