Hi techmattr,
I have also had an issue with “symptoms” on a particular memory foam topper (not Tempurpedic) but I have slept on many other types of memory foam as well without experiencing any symptoms (see post #2 here). If your wife is still experiencing symptoms 7 years later then it’s very unlikely that they were caused by the memory foam because in almost all cases any symptoms that come from sleeping on memory foam will resolve themselves within a week or so (and usually less) after you stop using it.
While it’s uncommon for any mattress to develop mold issues … if there are a combination of risk factors that affect humidity and ventilation in a mattress then it can make mold issues more likely. Tempurpedic uses a solid surface foundation that doesn’t have any ventilation and this in combination with other risk factors can certainly contribute to the formation of mold … especially in the bottom of a mattress (see post #10 here). With a foundation that provides better ventilation under a mattress this would be very unlikely to happen with any mattress.
While there are certainly some benefits to using organic materials that can be important for some people for personal or lifestyle reasons (see post #3 here) … in many cases non organic versions of the same material (with latex and wool especially) can be just as “safe” and free from chemicals and have the same properties, performance, and durability as their certified organic counterparts. There is more about the different levels of organic certifications in post #2 here. There are also many mattresses available that use all organic materials and fibers that are in much lower price ranges than the prices you mentioned if an organic certification is an important part of your criteria outside of the safety of or any “chemicals” in the materials themselves.
Phoenix