Here it is! Doesn't look anything like the designs I was previously testing out, but I'm very happy with it. I had a revelation that I needed to use a design that conformed more closely to the nine-patch instead of looking superimposed on top of it.
Luckily, Eva Larkin gives lots of advice in her book on how to adapt her quilting motifs to your blocks, so following her instructions I played around on photoshop until I came up with this. You can see my stitching isn't super exact, but I bet I'll be really good at those curves by the end of this quilt. For now I'm drawing in all of the curves before I stitch them because I don't trust myself to make them symmetric just doing free-form.