When is it okay to add a blanket in your baby’s crib?

I am a FTM my baby is 7 months. She hasn’t slept with a blanket or anything in her crib ever. The only time she has a blanket is when she’s in bed with me and i’m able to watch where the blanket goes or during nap time i’ll give her a blanket cause i’m awake and able to watch her through the monitor. My baby rolls a lot in her sleep so it makes me nervous... But it’s getting cold at night (We live in NY so i’m talking 30 sometimes 20 degrees at night time outside.) and I always try to make sure her room is at 70 degrees during the night but when i’m sleeping it drops to sometimes 66. and I feel so bad. I don’t want her cold. I do have her sleeping in a warm sleeper all the time but it just makes me sad... I was thinking waiting until she was 1 years for a blanket but i’m second guessing it....

So enough rambling, When did you give your baby a blanket for bed time?

THANK YOU EVERYONE! I’ll definitely be looking into buying her a sleepsack!