When mine are little I have them in the crook of my arm also. The weight of them is enough to remind me are there, & I never let myself cet comfy enough to fall into a really deep sleep iykwim. I have her in the cot next to the bed atm, since she sleeps through in there, but if DH is at work (leaves at 4am) & she wakes she comes in with me.
Don't trust DH with her in there just yet, even though my last 2 were in there from only a few days old. Also, DS is in our bed alot & moves around way too much, kicking & stuff for me to have her near him, lol.
Friends of ours have 2 boys co sleeping & have a cot on either side of the bed with the side closest to the bed off the cot. They also have a king size bed, so that helps. But with the cots there they can move them in & out of the bad as needed, but they are still sleeping with them iykwim.