How do you topstitch knits?

[Kori]

I know many of you coverstitch. I don't have a desire to buy or use one.

A single straight stitch always looks best for me and I've never had a problem with it breaking. Maybe it's because I make my neck openings big enough so they don't need to stretch much. I feel like it's not professional though so I don't know if I should sell anything like that. That's why I use RTW shirts in my outfits but I want to start creating and selling with some of my cute knit print stash. My double stretch needle never looks good. I don't know what I'm doing wrong but I get that puckering between the stitches. Sometimes I don't topstitch at all which looks fine as long as it's ironed. I tried doing a zig zag tonight and it looks okay. I can't get any topstitching to work on stretchy baby nay or baby lulu. Even some I have that were coverstitched get all stretched out.

Tip, ideas? What do you do (besides coverstitch)?