I would do a simple 9 patch, or add a third color and make a DP9. i often tie flannel quilts, have not had any issues with the ties not holding. if you do a rag quilt, batting could be added to the center for a really warm quilt. Example, 8 in. sq. of flannel with a 6in. sq. of batting for center. Sew "X" thru the square to hold batting in place.