Hi nodnarb,
I’m not aware of any specific chemicals that would be used in most of the foundations used in the industry that most people would consider toxic or harmful although of course some people that are more sensitive to certain materials or have some type of health condition (such as multiple chemical sensitivity) may be more sensitive than others to some of the substances or materials that are used in some foundations or box springs such as some types of glue or any treatments that are used for the wood (although most of the chemical treatments used for wood would be for outdoor use) so this would depend on knowing the specifics of a particular foundation. Some people may also have some level of concern with offgassing issues that may be connected with the use of some types of engineered wood or plywood.
For those who have more stringent criteria for choosing a foundation that are different from the concerns or criteria of most other people then they may need to do much more detailed research and make choices based on much more specific information about any particular foundation that they may be considering which may be much more difficult to come by or find out. Once they had the more detailed specifics (if these were available) that they required that would allow them to to identify any particular materials or “chemicals” that they wished to avoid that they believed could cause them harm then they would be able to make a buying decision that they were comfortable with but this type of research can be very frustrating because you may not have access to all the information about any product that you may need to help you answer “how safe is safe enough for me?” to the degree of specificity that may be important to you.
Knowing this would depend on knowing the specifics of the materials and design of each foundation but in more “real life” terms if a mattress you choose needs a firm non flexing support surface and two foundations provide this equally and neither one has wide enough “gaps” in the support surface to allow the materials in the mattress to sag into the gaps over time and they both use similar materials and would maintain the firmness and evenness of the support surface over the same period of time then they would be equally suitable for a particular mattress. There is more about the different types of support systems that are generally suitable for different types of mattresses in the foundation post here.
As you can see in post #10 here … I would tend to agree with your concerns about the risk of having no airflow under a mattress but I’m not clear on why you stopped using the platform bedframe that you were using because I don’t know of any reason that would cause me any concern with toxicity and most of these types of support surfaces would be suitable for your mattress.
If you get a foundation (not a box spring which flexes and wouldn’t be suitable for your mattress) then a metal bedframe with good center support would be a suitable choice. I would tend to avoid using a foundation on top of one of the wire grid platform frames because they aren’t designed to be used with a foundation on top of them and the combination may not be stable, may shift or wobble, or make noise if they aren’t a perfect match at all the load bearing points between them and there aren’t any edge supports to keep the foundation from sliding. It may also be higher than you would prefer. I haven’t tried this and don’t know of any feedback from someone who has but if it provided a firm non flexing and stable support surface then from this perspective it would be OK but it’s not a combination I would choose.
Phoenix