Here’s an example of a wool batting that comes with a thin spun backing, which is also wool:
A backing makes it possible to secure your batting without the use of glue. It needs to be strong enough to enable either hand stitching or plier-stapling around the edges of your latex foam core, and to hold up to stapling (with care) to wood in tight upholstery.
If you purchase a wool batting that does not have this backing, you can use a thin fabric to serve the same purpose. I like to use open weave cotton such as gauze or harem cloth for this purpose, but a thin muslin could work as well.
For instructions on how to cut and ‘book-wrap’ your foam with the most economical use of wool, check out this video.