I use Grobags. They're foolproof in that they are rated and tell you what clothes to put on bub with which particular weighted bag (there are 3) for what temp the room is. With Oskar I found I had to have one extra layer than they said but Elijah is a hotter kid and usually has what they say or a little less. Took so much guesswork out of it. Polar fleece can be quite sweaty and hot as it doesn't breathe so well. If you find grobags too exy you can find them also on eBay and there are online ones which are selling out. I've always just bought them from the baby shop and on my second bub with them and they're still in fabulous condition. So, I think worth the money.