Hi cassandram,
The definition for “environmentally friendly” is quite nebulous and can apply to multiple stages of foam production that are beyond the scope of this forum, and in general it’s something that tends to be defined by each individual according to their area of focus and own personal definitions.
“Toxic” is a term for poisonous substances produced within living cells or organisms, although the term is often used in the mattress industry (and often part of some “fear-mongering” campaigns). Most people that are looking for “non or less-toxic” (toxicity is dose-dependent) materials are usually concerned most with “safety”.
There is quite a bit of confusing information available online about toxicity, safety and organic, and there is more about the different types of organic and safety certifications such as Oeko-tex, Eco-Institut, Greenguard Gold, C2C, and CertiPUR-US in post #2 here, and more about some of the differences between organic and safety certifications in post #2 here and there are also some comments in post #42 here that can help you decide whether an organic certification is important to you for environmental, social, or personal reasons, or whether a “safety” certification is enough, and what those certifications can mean to determine whether the contents of any particular mattress are “safe enough” for you.
If you desire to stay with a memory foam product, based upon your statements you’d probably want to look at something that would have at least a CertiPUR-US certification (this is for polyfoams and memory foams).
Latex is generally able to meet more stringent standards for VOCs and harmful substances, and if you decide to move in that direction, but still desire the slower recovery feel of memory foam, there is a form of slow recovery latex available called Puralux. You can create a mattress using it in a component-style system such as here at Mattresses.net (they are a site member here and experienced with this particular latex foam).
In general, those would be two directions for you to pursue. Memory foam has a very specific feel and is not very resilient (bouncy), so there are not many types of products similar to it.
If you have more specific questions after looking through this information, I’ll do my best to answer them.
Phoenix