I loved having a co-sleeper bassinet, so we got the closeness of bedsharing, but the baby had his own space. I was too paranoid with them actually in our bed and couldn't sleep well. I followed all the co-sleeping "rules," but woke up once with my arm over my baby's head, pushing his face into the mattress. He was fine, but it scared the heck out of me. The co-sleeper made for good sleep for all of us. If you're going to do a floor bed, think about getting a real Japanese futon. They're firm, surprising comfortable, and low to the ground. You won't get the wedging issues that you might with a regular mattress, and all cotton doesn't off-gas.
The one thing that I do think is really unsafe is to leave the baby unattended napping on a full-height bed. Yeah, maybe they don't roll...yet. Some pick it up awfully quickly. I know of several very small babies who fell of beds that way, one of whom broke a leg. Another was fine, but ended up being kept overnight at the hospital for observation. It's so simple to have a bassinet, a basket, or something else that you can tuck baby in, or even a blanket on the floor.