Hi, try going to diverite.com and use thier solution finder help system or download the fitting guide and if that fails call them. I distribute Dive Rite and belive me a Transpac will fit anyone if set-up correctly, from 10yr olds to Macdonalds customer of the year. Your local stockist should have a copy of the Transpac promise video which is easy to follow and adresses ladies fitment.
I teach and dive recreational and tech and I would never consider a backplate for single tank diving, I know it's fashionable and looks "tech and cool" but it's innificient, places the cylinder as much as 2" off your back depending on single adaptor. Remember, rigs without buckles need a bit of extra rescue and operational training for you and your dive buddy to learn removal drill. Good luck I hope you find something that works for you whatever it is.