Hi alpharalpha,
Off my head, here are a few:
https://sleeplikeabear.com/product/natural-wool-quilted-bamboo-zipper-mattress-cover.htm
https://sleeplikeabear.com/product/Pure-Certified-Organic-Cotton-Zipper-Mattress-Cover.htm
You can also look at the cover suppliers listed in the component post here.
Phoenix