Hello! My son (who is 5 months in a week) can’t quite roll yet (he can go sideways but cannot roll tummy to back or vice versa without assistance). He has outgrown his bassinet which has been next to our bed at night and his cot (where he has daytime naps under supervision) will not fit in our room, Is it unsafe to move him into his cot at night time when he cannot roll yet? I am unsure what to do and am contemplating sleeping on a blow up mattress on the floor in his room so he can sleep in his cot. Thanks

Most babies begin to roll, or attempt to, by about 4-5 months of age.
It is not unsafe for him to move to a cot - in fact it would be recommended for him now, for all sleeps.
Some babies go to a cot from birth.
Maybe even “going sideways” is an attempt to roll, but he doesn’t have the space to do so.
Are you still wrapping/swaddling him? ...... if so, then I would suggest you cease wrapping.
Babies need arms free & the space of a cot to roll well & safely.
How does he go with tummy time when awake?

**Increasing tummy time when awake is recommended to help build upper body strength so he can roll easily & well.
Always continue to place baby on back to sleep.

Red Nose has the following general information now that your baby is rolling. 
“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 toysAs 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.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

See link to info about room sharing,(esp 1st paragraph) including the following:
” Parents are not expected to observe their baby constantly. If your baby is sleeping in a separate room check baby regularly to ensure that the baby remains on the back and the head and face remain uncovered “

” The protective effect of room sharing can be partially explained by increased adult supervision and observation of the baby “
https://rednose.org.au/article/room-sharing-with-baby