What chemicals typically offgas from a conventional mattress?

That is a difficult question to answer, because every "chemical" mattress can be constructed differently and treated with any number of synthetic applications.

Our founder Walt Bader's books, Sleep Safe in a Toxic World and Toxic Bedrooms: Your Guide to a Safe Night’s Sleep, list more than 60 different chemicals as being emitted from a memory-foam mattress and 37 chemicals emitting from a typical innerspring pillow-top mattress. The vast majority of these chemicals are derivatives of petroleum and natural gas.