Hi mftbny,
The first place I would start with any mattress research is post #1 here which has all the basic information, steps, and guidelines that you will find most helpful.
Post #2 here also has links to some of the more informative and helpful forum posts about mattresses and children and links to some good quality and value sources.
Post #2 here has a lot more information and links about green, ecofriendly, safe, natural, organic and all the other related terms that are often used more for marketing purposes than anything else and in many cases can be as misleading as they can be helpful.
Phoenix