I am anything but a purist! Altho I try not to mix poly cotton and unwashed (unshrunk) cotton. Sometimes that 'absolutely perfect' coordinating fabric is a blend. I have even been known to double up broadcloth for sashing if it seems thin. I use whatever is available for piecing thread. Right now that is a very large cone of serger thread, and my machine doesn't seem to mind at all. Yes, it does seem to fuzz a bit more so I wind two spools at a time and clean every time I need to rewind. I prefer poly batting, especially for kids' quilts. But I also have 80/20 and pure wool. Just depends who the recipient is going to be.
Most of my tops go to our guild's community outreach program and they are phenomenal. We supply quilts for The Abused families shelter, the teenage Choices shelter, the hospice, the dialysis unit at the local hospital, Fire and Police services, plus many many quilts to people or families in need. I don't think any of the recipients are going to complain because the quilt they received was not 'purely cotton'.