How to know if your baby is too cold at night?

We keep our apartment between 69-75 at night and dress our baby in long sleeve footie pj's and a sleep sack. It was really hot over the summer so our AC struggled to keep our place at 76 even, but now that it's cooled down, it's usually more around 69 at night. I've noticed my baby's hands and cheeks are cold now when he wakes up, and he's started waking up more frequently this week.

So I'm curious, how are others dressing their babies at night and when do you know if they're too cold? Should I try out adding a onesie under his current setup? I've seen some charts about how to dress them for different temperatures but maybe my baby is getting cold more easily after only living in hot conditions so far?