It's easy to do wavy lines with a walking foot. If you try it on a test sandwich, you will find it's actually easier than trying to sew a straight line.
Aside from using a walking foot, starching both top and backing fabric helps a lot to prevent puckers and tucks. Using 505 basting spray also helps, as it keeps all 3 layers in continuous contact with each other. This lessons the ability of the fabrics to fold over and create a tuck.