Hi Debid,
Post #2 here and the topics it links to has much more information about mattresses and children and “safe” materials. It also includes a number of links to the better forum posts and topics about mattress and children as well (including 4 links to topics about crib mattresses) that can help you decide on a crib mattress that is the best “match” for the criteria that are important to you.
There is also more about the benefits of an organic certification in post #3 here and there is more about the different levels of organic certifications in post #2 here and about organic and safety certifications in general in post #2 here for those where an organic certification is important for personal, environmental, or lifestyle reasons that can help you decide whether a reliable safety certification is “safe enough” for you or whether an organic certification is also important to you.
While the polyethylene isn’t organic … IMO it would certainly be “safe enough” and would be a suitable firmness choice for a baby or an infant but I would also keep in mind that all the issues that are connected to answering questions about “how safe is safe enough for me” on a personal level can be complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, beliefs, and lifestyle choices so different people may make very different choices than others regarding “safety”. Just as an example I would personally be comfortable with latex, wool, metal springs, or “safe” synthetic materials but I also understand that there are also others that aren’t and that have different opinions.
Phoenix