Very simple pattern, worked in garter stitch throughout, plain back. Two small buttons for front closure.

My original prototype was made from 75% silk/25% cashmere machine knitting yarn which is nowhere to be available right now. The best substitutes could be Dale Baby Ull, 100% wool, 50gr/1.75oz/165m/180yds.
From my experience to be a success the yarn needs to have some bounce and memory in it, so at least some percentage of 100% wool is preferable.