Hi Lnr103,
If VOC’s and harmful substances are the main issue then the certification of the material would be the simplest way to make sure that a material is inside the range that most people would be comfortable with and consider to be “safe”. For memory foam and polyfoam (both of which are synthetic materials made from petrochemicals) CertiPur is the most common certification for harmful substances and VOC’s and with latex Oeko-Tex is the certification that you will see most often and is a little more stringent than CertiPur. All the latex you are likely to encounter is Oeko-Tex certified whether it is 100% natural, synthetic, or blended latex and all of it would be “safe” by most people’s standards.
Of course some people may have some health or medical issues (such as MCS or multiple chemical sensitivities) that make them more sensitive than others to some materials or for personal reasons may wish to avoid synthetic materials completely and for those where their answer to the question of “how safe is safe enough for me?” is different from the majority of people then post #2 here and the links and sources of information it leads to may also be a good place to start the research into the much more detailed, complex, and often misleading and contradictory information that is all over the web connected to the relative “safety” of mattress materials and fire retardant methods.
I guess that eliminates horsehair as an option in your mattress :). Fortunately it’s only found is some much higher budget mattresses.
Phoenix