Hi Flana,
Post #2 here and the posts it links to has more information about safe, natural, organic, “chemical free”, and green mattresses and mattress materials that can help you sort through some of the marketing information and terminology that you will encounter in the industry and can help you differentiate between them and decide on the types of materials you are most comfortable having in your mattress and help you answer “how safe is safe enough for me”. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, and lifestyle choices.
There are three types of foam (either polyfoam, memory foam, and latex foam) so I don’t know which type of foam they are referring to but “open cell” foam means that the foam will typically have a higher airflow which improves its ability to regulate temperature although it’s usually used more in a marketing sense than a technical sense because they will rarely provide any specific information that compares the airflow of the foam they are referring to with other types or brands of similar foam.
It sounds like you are at step 3 of the mattress shopping tutorial which means that the next step will be deciding on the type of mattresses and materials you are most interested in testing and then visiting the ones that carry mattresses that meet your criteria and that you are most interested in testing.
There is more about the different ways to choose a mattress (either locally or online) in post #2 here that can help you identify and minimize the risks involved in each of them and there is also more about the most important parts of the “value” of a mattress purchase that can help you make more meaningful comparisons between mattresses.
Post #13 here also has more about the most important parts of the “value” of a mattress purchase that can help you make more meaningful comparisons between mattresses.
Post #2 here includes links to most of the better forum posts and topics about mattresses and children and includes some guidelines and suggestions that should be helpful.
Phoenix