I was thinking a celtic knot might look nice in the center, but I really like the flower that pagzz drew. So pretty. If you do go with the flower (that's my vote!), maybe a nice loopy, leafy vine would look nice in the teal border, and then repeat the star shape in the patched border. I found a nice clip-art leaf online & just printed it out & cut it out on template plastic for this little doll dresses quilt that I'm just sewing the flower yo-yo's onto now. I did them in 3 different colors like thread painting. Honestly, I couldn't be happier with it. They were super easy to FMQ once I drew it all out with Ultra Clean markers on my quilt.
No matter what, I'm sure the quilting will be every bit as beautiful as your quilt top. Nice work!!!