We cover this topic in more detail on our blog post - Mattress smell offgassing – How do I protect myself and my family?

Our solutions will help significantly reduce to contain, but not prevent, off gassing of volatile organic compounds (VOCs) from conventional mattresses - choose from 100% organic to using less offgassing plastic options.

Note that it's a challenge to find both organic material and waterproof together as to waterproof something, you need plastic and most plastics are also the source of off-gassing VOCs. 

If looking for pillow encasement that is Organic, dust mite / bedbug resistant (but not waterproof)
If looking for mattress encasement that is Organic, dust mite / bedbug resistant (but not waterproof) 

The best compromise we've found is this mattress pad which is  waterproof, dustmite / bedbug resistant - it's made with tencel, which is made from eucalyptus leaves but isn't considered organic; it's the more eco friendly option. It does contain 2% polyurethane film for waterproofing (Global Organic Textile Standard allows upto 5% polyurethane) and doesn't smell like it's offgassing either.