I woold use 19 and try a test sample to check the size. If it is a small piece you are appliqueing, use a smaller stitch. also, be sure to put a stabilizer under it to keep it from puckering. Just use a tear-away or something. LIke someone else said, be sure to stop (with your needle down) often and turn your work. Good luck - it will turn out great - just practice first.