Side sleeper

[Christmasbaby16]

So our baby is 20 weeks, has been rolling from tummy to back since 16weeks and from back to tummy for the past two weeks...he has always been an excellent sleeper (Lucky, I know).
For the past few nights he is rolling onto his side and sleeping like this. I gently out him on his back but in second he is back onto his side again.
Hes rather long for his age and has therefore been in his cot since 13 weeks (In our room, next to our bed).
Any ideas? Do I leave him to side sleep despite recommendations... I am constantly waking myself to check on him!

The guidelines state that you should always put baby down on their back. Once your baby can roll from back to front and back again, on their own, they can be left to find their own position once put to bed.