C.F.
Yup, there's no problem with babies sleeping on their sides. They just don't want them to sleep on their stomachs. No worries- if he looks comfortable on his side just let him be. They always say "back to sleep" but in reality, the side is just as fine. He is old enough to be able to roll over on his own now anyway, so even if he did fall asleep on his stomach it wouldn't be as big of a deal as the first 4-5 months.