Choosing the right mattress isn’t easy is it! As you mentioned the adhesives, constituents of synthetic foam and the fire retardants used in the manufacture of synthetic foam mattresses do contain many toxic chemicals, including petroleum based compounds. These chemicals can leach from the mattress via gas and dust release and expose your family to these toxic compounds while they are sleeping. A cotton mattress protector, dust mite cover, organic wool or latex barrier may provide a small amount of protection but it is possible that some of these harmful chemicals may still be released and result in exposure. Many of these synthetic or plastic covers will only add more chemical exposure and off-gassing to the situation. Some say that a thick layer of plastic such as Polyethylene is considered the safest, non-toxic plastic to use as a plastic cover to reduce toxic off-gassing. However using plastic has its own adverse effects such as noise and it is also a non-breatheable plastic which means that the mattress will not be so easily aired.