I think SIDS increase significantly when not sleeping on back. For naps try to reposition ok for safety. Always on back with no blankies pillows toys near mattress or in the crib. Sideways might be ok but do check with peads alot of updates
Because he is able to turn himself back. let him be. sometimes you shift also will disturb his sleep. just remember no pillows toys or blankets surrounding him. just plan flat firm mattress.
I’m no expert but my baby sleeps on her side and she’s fine. Now she’s 10mo and sometimes she prefers to sleep tummy down and we let her, but we make sure there’s no blanket.