Another thing to consider is the thinner the batting the more problems you will have. There is less space for the threads to connect together in the center. I have been working with wall hangings for 2 different clients and used Quilters Dream deluxe weight cotton batting and had good results with different top and bottom thread. Another thing that can make a difference is the thread count of the backing and quilt top fabric. LQS fabric will usually be of a better quality.