Hi awoods,
I don’t know anything about the companies you mentioned but some of the polyfoam sources that are listed in the components list here sell polyfoam in any size, shape, density, and firmness you may need and would be a good source of guidance for what to use for an ottoman as well. A1 foam and fabrics, Foam online, and Foam order all sell polyfoam in different densities and firmnesses in the shape you are looking for and some of the others may as well.
Phoenix