Three things which will help avoid the dreaded shifting.
Use a cotton batt, as already suggested, Warm and White is good, so is Quilter's Dream.
Use a walking foot for your straight line quilting. Mine improved 1000% when I started using a walking foot. They're expensive, (the one for my
1992 era Bernina was over $100), and worth every last cent.
Another thing I have seen suggested a couple of places but have not yet tried is to baste with water soluble thread. That way, you have the advantages of thread basting, and it just dissolves away when you are through.
Good luck, and do let us know how it turns out.
Becky