Hi, my 16m old daughter has always slept in a sleeping bag and has always been a great sleeper. But I'm thinking of getting her a proper duvet, they look warmer. I'm very interested in the snuggle sacs, for those who are familiar with them (for those who are not, they are basically duvets with zips on each sides, great for wriggly toddlers like mine). The problem is I don't like their designs, and you can't fit covers around them. Is there another similar concept out there?