Bedsharing mamas- with mattress on the floor, do you need a barrier on the side?

We are planning to bedshare with our newborn, my husband is a heavy sleeper and neither of us want our son in the middle of the bed near him. We are planning to have baby beside me on the outer side of the bed. Not planning to use a basket or cosleeper (I have one in case we decide we want to try it, but taking baby in and out of a basket takes away the draw to breastsleeping for me). I've read many options for making baby being on the outer side of the bed work, including up against the wall with some sort of buffer to block the crack, bed rails, and putting the mattress on the floor. We already have our mattress directly on our floor so we plan to keep it that way. The mattress is maybe 6-8 inches high (it's not an inter spring it is a firm foam/ gel type). With the mattress on the floor, do I still need to use something to buffer the edge of the mattress to keep him from rolling off? Could I push the mattress up against the wall and just make sure it stays firmly against the wall? Any suggestions or advice would be appreciated!