I would like to have/make some mats to go on the floor next to the indoor trampoline and also to go under the climbing wall my husband is building in the play room. I'm concerned about flame retardants and other toxins in new foam or gym mats. Any ideas? It would be easy to sew canvas or an old blanket to make a mat cover. Anyone have any ideas of what would be non toxic to stuff it with? I would prefer something reused but any ideas would be helpful!