I've posted this before - but what worked for me is when I measured my sitbones, I did so by sitting on a piece of paper on top of my Pilates mat, on top of a concrete step, with my pelvis approximating my riding position. Then I took a felt-tip pen and outlined the indentations on the piece of paper.

I had a pretty good idea of what saddle I wanted just from reading the threads here, but before I bought it, I brought my butt-print to the LBS and laid it on top of the saddle. So I could see whether it was going to support my sitbones, or whether it curved away from me in a way that wasn't going to work. A portable, flexible butt-print plus the hard chair cut-out test goes a long way, IMO.