Hi gardenguy,
All foams will need protection from the mechanical abrasive forces, outside added materials (body oils, skin cells, fluids, etc.) as well as protection from UV rays and oxidation. Most foams will already have anti-oxidants blended into them, but you’ll still want to use a good covering. There are a myriad of mattress encasements available, with the most flexible generally being some sort of a cotton/polyester/viscose blended with something like elastin. These will interfere less with the point elasticity of your very soft latex later.
You’ll always want a good mattress cover for protection from wear and “the elements”, as well as helping to hold the materials together. DIYNaturalBedding had some interesting comments a few years ago about some of their latex samples and noted that the latex using a double wool batting and cotton cover showed the least amount of discoloration, followed by their latex using a single layer of wool with a cotton cover. Both showed minimal discoloration (some of which of course is normal). Of course your mattress will also have a mattress pad, fitted sheet, flat sheet, blanket and comforter upon it during the day as well. I’m not familiar with the encasement you’re describing, but maybe someone here on the forum here is and can provide you some feedback.
If you want to look at some other options, you may wish to look at some of the cover suppliers listed in the component post here.
Phoenix