A baby can get tangled up in a blanket, making it unsafe. Instead, experts recommend sleep sacks to keep babies warm while they snooze. “A sleep sack is simply a zip-up ‘bag’ that your baby ...

I would err on the side of buying bigger rather than smaller so your baby can grow into it, and you can make sure you're not restricting their legs or hips with a sleep sack that's too snug.