Hi smmimp14,
I’m sorry to hear about your issues with your polyfoam topper. Something at that density and ILD (rather firm for a topper) should hold shape for some time under normal use when placed upon a mattress that isn’t sagging.
For some sources of which I am aware for polyfoam, you can take a look at the component post here and scroll down to the polyfoam section. While this is not of course a complete list, it should help to give you a good start.
Phoenix