I'm really interested in people's experiences with cotton/wool crib mattresses. We are debating buying one from Organic Grace, but I've read that mold can be a concern in mattresses without waterproof coatings. Since this is our first child, I really have no idea how likely it is that the mattress will get wet enough to develop mold. We would use a wool pad between the sheet and mattress to help absorb any moisture, but would this work well enough?
We are also considering the Naturepedic organic mattress, but I'm really not wild about the plastic surface, even if it is supposedly non-toxic.
We have this OMI organic latex crib mattress and love it. We've used it for two babies now, and we've never had a problem with mold or mildew. I thought that was one of the reasons why wool and latex were so great -- because they were antimicrobial!
To answer your second question, we use a wool puddle pad over a thick cotton flannel mattress cover. Nothing from either baby has soaked through the wool cover onto the flannel cover. When I brought the wool puddle pads out of storage before my son was born, I washed the pads in a lanolin soap and sprayed liquid lanolin on them to make sure they would be water resistant. So far, I've had no problems. Even though the wool has worked really well for us, I would still feel more comfortable having the flannel mattress cover over the mattress. The organic crib mattresses are so expensive, I didn't want to risk any problems, especially since I knew we would need it for multiple babies!