After a lot of research, I bought a Naturpedic lightweight. I did the research a while ago so the specifics are escaping me right now, but it doesn't contain the materials that cause concern over off-gassing. The covering is food grade polyethylene. There are no regulations governing the use of the word "organic," so many so-called "organic" mattresses are BS.
Re: Organic Crib Mattress
I was told the Essentia mattress is the only true organic foam mattress? its pricey though... still debating it.
Nook Pebble Organic would be my first choice