What is the best baby sleep monitor?

My four month old daughter has recently mastered rolling over to her stomach and to her back but only going in one direction. She now refuses to fall asleep on her back and will roll herself to her tummy. I’m worried of SIDS. Everything is free from her play pen of course but I’m worried of her only rolling one way she will get stuck against the side. Any recommendations on sleep monitors? How well the alerts work, what it monitors, and how it attaches to baby?

There is a monitor that attaches to the babies foot. It monitors breathing will alarm you if it stops…. I forget what it is called

Owellet sock I believe is what is called