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.