I'm with cjsews. I think a black border will be too harsh since the fabrics are kind of muted. Some of the blocks have a little gray in them and I think that would be a perfect border with maybe a creamy colored thin flange to stop the eye on the edges. The quilt is lovely just as it is, and if you could find some old house dresses to add blocks would be a way to make it larger. Shop around, maybe just the fabric is right around the corner waiting to be found. Good luck. I'm glad you were able to rescue the quilt.
Sue