I love your quilt. I think any thing you come up with to quilt it will be beautiful.

I think your focus should be on the stars, so stitch in the ditch around all the stars then some kind of wide filler for the solid background area using a thread that matches. Since there are points and some open areas you could do like a teardrop shape or keep with straight lines and use the pinwheel shape that appears in the space between the stars (the negative space).