Hi Bcgirl,
Using a wool quilted cover vs a thinner stretch knit cover has some “tradeoffs” and some people prefer one and some the other. It can slightly reduce the ability of softer latex to contour to your body but it also provides some temperature regulating benefits, a little bit less resilient sleeping surface by “damping” the resilience of the latex, and as you mentioned it can also be used as a fire retardant barrier in the mattress.
The additional snugsleep topper will compound the effect as well and can further reduce the contouring effect of the latex but provide more of the benefits of a wool sleeping surface.
It’s also true that the cover will loosen once it is broken in.
It may be worthwhile unzipping the mattress cover to see if this has an effect as well.
Do you mean the owner of Mattresses.net?. A stretch knit cotton cover will allow the latex to contour more but you would also lose the benefits of sleeping on the wool (outside of your snugsleep topper of course). If the cover is thick enough to be suitable for use with a mattress and protects the latex from light and ozone (which are the main “enemies” of latex) then it will be fine and your mattress protector (or snugsleep topper if you decide to use it as a mattress protector) will protect the mattress from moisture and from the skin particles that dust mites feed on.
If you want additional protection from dust mites because of more severe allergies then you can also use a thin mattress encasement but latex is already more dust mite resistant than other types of material (see post #2 here).
Phoenix