American Wellness protectors
I bought a PUL protector from American Wellness Supply (awshealth.com) that is mainly designed to keep bedbugs out, but it does a good job of keeping liquids away from the mattress also. It's supposed to be machine-washable and -dryable, but after a couple of cycles of drying it began to leak massively. The protector is guaranteed, so AWS sent me another one (after seeing a pic of the resulting large spot on my mattress!). In the future I'll wash it occasionally but not put it in the dryer, even on the Delicate setting. The protector doesn't crinkle, even though it's not cloth on top.