I know it's not recommended but I've got a seven week old who will only nap in sling, which is fine, but every now and again, I really need to get cooking done for ds1 or just feel like my back needs a break and I've discovered that if I pop him on my bed on his tummy, he has a really good nap like that. It doesn't work at all if I put him down on his back. I keep a good eye on him. Has anyone else done this? Do you think it's really bad? He sleeps on his back at night.