Non Toxic Crib Mattress

Hello everyone!!! My daughter is now 16 months and we've co-slept with her (in our firm bed) since day one. We are ready to transition her to a crib. We have the crib but haven't purchased the mattress yet. I'm looking for recommendations on non-toxic crib mattresses - there is so much information out there that my head is officially spinning.

Also, since she is 16 months, just how firm of a mattress do we need to purchase at this point?

Thank you for all opinions and advice!!

EDITED TO ADD: Everyone... thank you so much for all the suggestions!!

Brenda