First of all, love your quilt!
Second, when I do memory quilts, I don't like to quilt over the "pictures". So I do a lot of ditch quilting on mine. If you want to add something a bit fancier, you could do something in the sashing like a curlieQ or tiny free motion hearts. It's hard to tell how large your blocks are, and that will factor in too depending on how far apart you need to quilt for your batting.
Good luck and I'd love to see a finished picture when you're done. :-)