I put the baby monitor right next to her and pillows all around her. I turn the volume up real loud and run in if I hear even the slightest sound. We live in a small house so this is easy.
We haven't had a problem yet!
this is exactly what we do. dd is now walking/running. we put the mattress and boxspring on the floor and have a guardrail on one side of the bed, and put pillows on the other.
when she was smaller (she's 17 months, now). we would place a noisy toy/rattle on each pillow, so we would hear the instant she contacted any of the pillows (or picked up a toy to play with it
)--but that didn't happen, really, 'cause as soon as we heard a sound, we'd investigate (we still do)
good luck, i remember fretting about this, too.
i would be cautious about putting pillows on the floor around the bed, in case he rolled off in his sleep and landed face-first in a pillow (it has happened in baskets of laundry