quick question for cosleepers

we don't cosleep at night, however, during the day I lay down with her in our bed to nurse her before her naps and when she falls asleep i sneak away.  She is getting really close to crawling and I am afraid she is going to take off one day and crawl right off the edge!  I block the edges with pillows but i know a pillow won't stop her much longer.  Is there anything I can do to make this safer other than put my mattress on the ground?  I am working on getting her to nap in her crib but feel i'm running out of time.