How complex and how much piecing do you want to do? When I saw the picture of this beautiful quilt and you wrote you had more of all the turquoise shades you used it I immediately envisioned a bargello type border done in all the colors you used in the quilt. I would put a very narrow border (maybe only 1/2" finished) of maybe the darkest turquoise than a pieced bargellow on the outside probably around 8". A lot of work, but I think it would be stunning.