how to keep baby warm at night?

Abbie
She has a sleeper that covers her feet and hands. She is 3 weeks. It's 70-73 in my apartment (pretty sure it drops a little during the night) I was swaddling her but she rolls over. I don't want to use any over loose blankets - she kicks around and it will end up at her head. I have q sleep sack but she doesn't fit in it yet! How to keep her warm??