I'm not a "scrappy"type quilter but I think if it were mine and I needed to add a border to finish to a desired size I would audition one made from all the fabrics I used in the design. I think my first possibility would be differing lengths pieced together diagonally with a small consistent piece from the sashing fabric acting as a "cornerstone" in between each pair of diagonally cut pieces. Am I making any sense? Sorry really tired tonight. My 1st choice would be no border if not needed to reach a certain size. Beautiful quilt!