DS slept on his tummy from an early age... a couple of months i think. He was rolling this way himself. I would roll him back and he would end up back on his tummy.
I used one of those roll cushions, but he would just scream until i took it away.

I contacted the SIDS help line, and they told me when they want it, they want it. You just have to be careful and keep a close eye on them if they are not really rolling yet - which wasnt the case for us.

Good luck and try not to stress too much