Hi Raphy,
Oeko-Tex is just a testing protocol that can test any material for harmful substances and VOC’s. Almost all the latex foam you will encounter is either Oeko-Tex certified or Eco-Institut certified. The most common certification for polyfoam or memory foam is CertiPur but there are a few that are Oeko-Tex certified (mostly European).
I would keep in mind that “green” has little to do with safety and more to do with the carbon footprint of a material from cradle to grave and its effect on the environment. Almost all materials will have some VOC’s and some of the worst VOC’s don’t have any odor and some that have an odor aren’t harmful at all so the certification of a material a much more reliable way to know how “safe” a material is than our sense of smell. I’m not sure how old your children are but I would also be very cautious with memory foam and very young children (see post #2 here).
Each person can be very different in how their weight is distributed and their preferences and specific sleeping positions so your own careful and objective testing will be important . For combination side/stomach sleepers then “just enough” softness and pressure relief for side sleeping and no more would be less risky for alignment when she sleeps on her stomach). If local testing isn’t possible on a specific mattress then a more detailed phone conversation with a knowledgeable and experienced online supplier that has your best interests at heart is the most effective way to decide on a mattress that has the highest odds of success (see mattress firmness/comfort levels in post #2 here).
Latex foam is very different from memory foam which in turn is very different from polyfoam so there will be thousands of variations of “foam” mattresses which will be very different from each other just like there would be thousands of variations of innerspring mattresses. “Foam” is just a generic or non specific term which means a material with bubbles in it just like “fruit” is a generic term. I would also keep in mind that you would also be sleeping on some type of foam with most innerspring mattresses (an innerspring is just a support layer not a comfort layer and usually has layers of foam above the innerspring).
The tutorial post has a link to a list of retailers and manufacturers that ship across Canada (both from Canada and the US) that include several that sell latex or other “foam” mattresses. Some of these are component mattresses that allow you to customize the mattress both before and after a purchase.
There may also be some good local options available to you and if you let me know your city or postal code I’d be happy to let you know about any of the better local options or possibilities I’m aware of.
Phoenix