Nope it doesn't matter just make sure he don't suffocate himself. Also u can use mustard pillow or u get baby pillow in market.

Babies sleep according to their comfort. My baby used to sleep on side until he was 4. As my pediatrician told it’s totally normal. Let them sleep like they want. If you’re afraid please make him sleep straight once he’s fast asleep. You can use u shaped pillows too

Thanks both of you

Babies tend to sleep like that, you change the side.

It's better to sleep straight .. try to get the posture after the baby is asleep as the shape of the head changes at times.. also use a mustard pillow.