M.V.
Definitely use a blanket! My daughter has been using one since about 7 months old. It is now her lovey and she cannot sleep without it. It's too cute! Personally, I think the sleep sacks are for the first six months or so. They cannot move around in them and seem to be a restriction to me! Especially when they're mobile. :) My daughter positions her blankie how ever she wants. And puts it on herself when she is cold (she is 11 1/2 months). By the way, hers is a crocheted blanket. When it gets cooler we will also add a warmer blanket and then she'll have two.