My 4 month old babe can now confidently roll from back to tummy, but not the other way. I've moved him to his cot where there is more room but now he's running in his sleep then waking up uncomfortable wanting to be turned back over. Two questions: 1. He doesn't seem to roll in his bassinet as it's a bit too small. Is it safe for him to sleep in it? 2. Is there anything I can do to keep him on his back overnight until the stage where he can roll both ways? The interrupted sleep and the worry is a bit of a problem. Thanks.

Most babies will be rolling over by 5 months…....some earlier, some later.

This is very normal as babies grow & become stronger many babies then prefer to sleep on their tummy, & often don’t change from that position.
Does he roll from tummy to back when awake doing tummy time?

It is important that you move your son from bassinet & cease wrapping if you have not already done that.
This is not something that needs to be stopped, but it is important to make the environment as safe as possible for this to occur.

Always place baby on their back to sleep.
Ensure cot mattress is firm, well-fitting & flat.
Ensure there is nothing loose or soft in the cot.
Preferable to use a sleeping bag now that has appropriate size neck & arm holes.

Red Nose has the following information now that your baby boy is starting to roll.

Give baby extra tummy time to play when awake and supervised as this helps baby to develop stronger neck and upper body muscles which in turn enables them to roll back over.
Make sure that baby is on a firm and well-fitting mattress that is flat (not tilted or elevated).
Make sure that baby’s face and head remains uncovered (do not use lambswool, doonas, pillows, cot bumpers or soft toys)

As babies grow and develop they become very active and learn to roll around the cot.
At this time, continue to put them on the back at the start of sleep time, but let them find their own position of comfort.
By this stage it is not necessary to wake during the night to turn baby over to the back position

Do not use any devices designed to keep baby in a particular sleep position.
https://rednose.com.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over
https://rednose.org.au/article/is-it-safe-to-use-products-designed-to-keep-baby-in-a-particular-position