I recommend a layer of wool batting between the latex and the cover fabric, for three basic reasons:
provides an added layer of protection for your latex foam from UV exposure
recognized as a NATURAL flame barrier that meets the revised CA TB117-2013 standard for flame retardants in upholstery
softens the edges of your cushion (as conventional polyester batting does in standard upholstery practice)
provides enough coverage to prevent the latex holes from showing through the cover fabric.
You can read more in this blog post.