lots of people use pearl cotton to tie their quilts...i was taught that a hand width apart is the spacing, a big needle...i had not heard anyone having a problem with their flannel falling apart with a few washings...i have grandchildren with flannel quilts 10+ years old been washed thousands of times and i have not had to do any mending...so that part has me puzzled...maybe used homespuns, not flannnel? or could just depend on where the flannel comes from, like with all fabric, not all is created equal. i spend alot of money on flannels, the most expensive quilts i make, but they are worth it, they get softer/fluffier everytime they get washed. did you pre-wash your flannels? if so, were they very limp/thin after, or are they thicker/softer? you will have to decide if they need to be quilted or should hold up to tying.