Around 5-6 months I started letting DS tummy sleep. In the meantime, I had some great little sleep wedges I used to prop him on his side instead. He couldn't roll over at first, and when he could I knew I could remove the wedges as he could roll back and forth. Imagine two toblerones sitting side by side, lengths adjacent to eachother, attached by a flap of fabric. Baby lays on the fabric keeping the toblerones in place. LOL, sorry for the weird description, but that's what they reminded me of. Giant toblerones. I got it at Big W for about 20 bucks I think.