I don't like bag breathing with a paper bag -- it's so scratchy. Can I bag breathe with a cotton bag? And if so, does it have to be non-porous? And what size should it be? I have no real experience with bag breathing, so I'm not sure what I should be doing with the bag. And does anyone happen to know of a place that sells cotton bags for bag breathing? That would save me the trouble of having to make one.