Personally, I lie on my side, facing towards the middle of the bed, and have my baby sleep in the crook of my arm ... have done it with all of my kids. If you like, you can lay pillows down the other side of the bed, but at Bella's age, I don't think she is likely to roll too far and she would be more likely to happily snuggle up to you and go back to sleep

I think it is all fairly instinctual when you co-sleep, whether it is for a few hours in the morning or all night.