Hi Frosty.
Sorry for the delayed reply! Phoenix cautions against using Foam By Mail and suggests reading this post and this post and this topic (about their polyfoam and sources) and this post (presumably from a past employee) before buying anything from Foam by Mail (AKA FBM and Foam Factory) or considering them as a reliable supplier.
Rockymountainmattress and sleepwarehouse have been used successfully by other members in the past searching for 5 lb memory foam toppers.
NikkiTMU