@BrendaP - Stretch stitch is a 3 step zig zag, with three stitches in each zag and zag, instead of just one. It's a curved shape on Bernina, like a wave (number 18 on the 230, which is actually called "lycra" in the manual), but some machines like Elna do it pointed. The shorter individual stitches means it pulls less and lies flatter on lycra than a regular zig zag.
I'd echo the stretch needles, not ballpoints - ballpoints are for jersey, not lycra, and I find that when sewing woven to lycra, it feeds better if you put the lycra on the bottom, so the feed dogs carry it along. I also have a teflon foot, but a lot of people like a walking foot.
For top stitching (eg over elastic) a plain zig zag is fine. Don't pull the fabric any more than you have to - pulling makes the stitches skip.