With Dorothy, I usually use man-made materials for her diaper covers. I have a real soft spot for wool though, and have used it to the exclusion of other cover material in the past with other children. There was a lengthy period where I had three in wool at once - that's where being a knitter is the most useful!
I have one wool cover for her, a Disana soaker. These are such nice covers! Here's Dorothy in hers, with a pinned prefold underneath.