I've seen these foam tiles (like giant puzzle pieces) that fit together and make a big crawling space for kids. We have hardwood floors and I'd love to get something our baby can crawl on without breathing in nasty chemicals... any suggestions?

I used my yoga mats, but don't know much about toxicity on them. My kids really like the puzzle piece mats. They get thrown like frisbees a LOT, though. Seldom are they on the floor... :)