Hi Alpharalpha,
Regarding covers, you already have a link to my listing of some of the better component suppliers of which I am aware vendors in the component post here. You’d have to phone the cover suppliers to see what they offer, as they often will offer items not shown on their web sites.
It’s common for latex manufacturers to use some filler in their product at a level that doesn’t diminish product performance but does lower production costs. There are many types of fillers used industry-wide. I believe feldspar was used years ago in some of the TG blended latex, but I’m not sure now.
It’s common for all foams, even latex, to soften with use over time. I’m not aware of any current “issues” with the latex from Talalay Global or Radium, and I would consider the product from both manufacturers to be a high quality and durable material.
Phoenix