I really like my Bummis pull-ons, and they've never come apart in the wash - you should definitely return them and get a/some new ones. I like my Lambkin wool covers a lot, and my Freshies Fittwrap (also wool.) I'm awaiting a soaker from Cushie Tushie, which I think will be great! HTH!
We use all wool, but before we used ME Airflows. Our favorite trim wool covers are sugarpeas and sugarbums. Both fit under clothing and fit over all our dipes, SOS, ME OS, cuddlebuns, etc.
Almst forgot Bumpy wool covers are good too, we outgrew the one we had though.
Sugar Peas wool -- love them! I also like my Angel Wraps covers.
BTW, you can try soaking your wool cover in a very diluted solution of water and liquid fabric softener -- it will soften it up quite a bit, and if anything, make it more water resistant. Worked great for me!