I was given a ball of the summer sock yarn as a gift. It is a bamboo/ cotton mix and very soft and fine. I cast on 120 st I think and did a couple of repeats of baby shale st to give the slightly scalloped edge.
I kept knitting till I got to the natural waist and decreased by CDD to 42 st. I left 8 st either side of the back parting, because the yarn is so fine.
Even with the extra st, the dress is still quite small, so I knit the bunny in merino extra fine on 3mm needles. It fits nicely.
I was going to line the skirt of the dress in blue net for volume, but I think that might make it too stiff and it looks OK without it.