I drag DD to the middle (she's always in the middle anyway, but when I was BF she'd be on whatever side I fed off), put pillows on the edges of the bed, and on the floor. Then pop the baby monitor on. DD is the type that will make a noise or cry before she gets up 99% of the time, and she also very rarely rolls by herself in bed, she wakes up and cries to be moved instead, so I've always been fairly happy that she won't fall out.