Go with natural latex, not memory foam.

"What is memory foam made of? Memory foam consists mainly of polyurethane with additional chemicals that increase its viscosity and density. It is often referred to as "viscoelastic" polyurethane foam, or low-resilience polyurethane foam (LRPu)."

"What is polyurethane? Polyurethane is a plastic material, which exists in various forms. It can be tailored to be either rigid or flexible, and is the material of choice for a broad range of end-user applications such as: insulation of refrigerators and freezers. building insulation. cushioning for furniture."

In other words, memory foam is basically a petroleum product.