You asked, so I will throw out my opinion, which is only a suggestion. I would add one border of the dark fabric used in the 9 patches, cut so it will finish the same width as the size of the 9 patch squares. Then I would audition bindings. Maybe use the dark fabric for binding too. If you need to add a 2nd border to make the quilt bigger, I would choose one of the green, blue or gold fabrics.
Beautiful quilt. Wonderful example of fabrics making the quilt.