Bonnie, your baby quilt is so cute!
I have used wavy lines a lot. I usually quilt diagonally, from corner to corner. Starting with a lazy, wavy line down the center, I just echo it, trying to stay about the same distance away. After finishing one direction, I start at the opposite corner and do the same thing...making a big, diagonal, wavy 'x' accross the quilt. But, I've never done a quilt larger than about twin size this way.
Just to change it up a bit, I tried a QAYG, and quilted the blocks with diagonal, wavy lines, using a wide and long zig zag stitch. (my walking foot has a wide opening, so this works with it). I really liked the effect.
Now, I zig zag a lot of my fmq...stippling, meandering, echoing, even bubbles and vines are fun with zig zag stitches.