Hi Zana,
I hope your treatments are going well and your health is improving.
Placing a topper, organic certified or not, on top of an existing mattress won’t change whatever VOCs or off-gassing might be happening from that product upon which it is placed. You’re not in direct contact with any of the existing foams in your current mattress, so using a new topper would only put you a few more inches away from your existing mattress, but it wouldn’t act as a “filter” or “scrub” any potential VOCs from your existing product. With your specific concerns, only the replacement of your current mattress would result in the minimization/elimination of any of the products with which you have a concern.
I certainly understand your concerns with your specific health issues, and I’m not a doctor of course so I’m not qualified to determine the potential cause for any health issue that someone may have (I’ll leave that to the health professionals), but if a polyfoam material is made in North America and/or is CertiPUR certified for harmful substances and VOC’s then I personally wouldn’t have any concerns about toxicity or other health issues (polyfoam is the same material that is used in most furniture foam). For those that may have unusual sensitivities or health conditions such as MCS (multiple chemical sensitivities) and wish to avoid synthetic materials that most people would be fine with then there is more information in post #2 here that can help answer their questions concerning “how safe is safe enough for me?”
I know I listed much of this information in a reply to a post of yours which was a bit similar a year ago, but for those who may be reading this for the first time…
There is a lot more information in post #2 here and the more detailed posts and information it links to about safe, natural, organic, “chemical free”, and “green” mattresses and mattress materials that can help you sort through some of the marketing information and terminology that you will encounter in the industry and can help you differentiate between them and answer “how safe is safe enough for me” that can help you decide on the type of materials and components you are most comfortable having in your mattress or on the certifications that may be important to you. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, beliefs, and lifestyle choices.
There is also more about the benefits of an organic certification in post #3 here and there is more about the different levels of organic certifications in post #2 here and about organic and safety certifications in general in post #2 here.
Phoenix