Since you don't have (any real) contrast, I'd suggest getting yardage of a multicolor batik that has those shades of purple in it, and 1/3 yard of two more purples to build variety of lights to darks. The other colors in the multi will help make the differences in the purples stand out more, and the other purples would give it more play. Also, the multi batik would let you play with another in it for accents - such as a center square (as in a log cabin, something small that pops), a very narrow inner border (or two) ... something like that.