Hello, 1. My son was a breech baby and has preferred rolling / sleeping on his left side since birth. He won’t seem to stay on his back for more than a minute or two without rolling. He is currently 7 weeks old and we still have him in a sleep sack with arms in. Should he be sleeping with his arms out given that he sleeps on his side? 2. I see that it is recommended that baby’s room share with their parents until at least 6 months of age but that they should transition to a cot (from a bassinet) once baby starts rolling. Our bun is currently in a co-sleeper and his cot won’t fit in our room. Once he starts rolling, should he be moved into his own room and into his cot? Or kept in his co-sleeper in our room?

1. Do you think is is intentionally rolling to his side or is he wriggling/squirming.?
Try him with his arms out & see if he stays on his back….. some babies like to have arms free to touch face &/or suck on fingers & they wriggle to try to get arms out.
If he is intentionally rolling to side, he should also have his arms out. He may not be long off rolling to tummy & back & changing his position - he would definitely need to move to his cot then.(if not before if rolling to side is intentional)
How does he go with tummy time when awake? Increase tummy time to help build upper body strength.
Still always place him on his back for sleep.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

2. Yes, it is important that baby moves to cot once he is rolling - baby needs arms free & the space of a cot to roll well & safely.
A safe environment for sleep takes priority over room sharing but parents are encouraged to check baby frequently when you wake during the night.
“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 (as baby grows beyond 5-6 months they will move around the cot and roll over; settle baby to sleep on their back but let them find the sleep position they feel most comfortable in. A safe cot and safe sleep environment is still necessary for babies older than 5-6 months).”
https://rednose.org.au/article/room-sharing-with-baby