It was like looking at my current project when I saw your string quilt. I am making scrappy quilts using the same pattern, but not including the sashing. I had been busy sewing squares when I took a break and saw yours.
A friend gave me a suggestion that I want to try. She used a Do-sew like product for her foundation so she could use a nice fabric for the center bar. She did a baby quilt and consistently put lavender in the center and pastels for the sew and flip pieces. She did this for color and so that her quality quilting fabric was not covered by the other pieces.