This is not as dangerous as you think. Make sure your child is sleeping on a relatively firm surface, without squishy bumpers on the sides, and the baby will be fine. But still, when you put your child to sleep, start with the the back.
Yes SIDS is a real danger, and there are indeed studies that show the risk increases when the baby sleeps on his stomach. But it's not like putting him in front of a moving train!
You cannot reasonably restrain your child while he is sleeping, nor constantly wake him to change his position.
It may help you to sleep better at night to consider this semi-logic: if the baby can roll onto his stomach, he's clearly got some strength and mobility, which is often 'said' to reduce risk of SIDS.
Focus on bigger risk factors, like the caregiver being under the influence, smoking, or being extremely tired.
Also take all the junk out of the bed, I sometimes see babies sleeping with ten stuffed animals and a giant pillow - stick to a firm mattress and nothing else. Use warmer PJs and avoid all but the lightest, smallest blankets.