I just want to note something about anatomical girths. The idea isn’t that an anatomical girth will make a saddle that doesn’t fit “work” (in some sense).
The idea is that sometimes, when a saddle scoots forward, it may not be because it doesn’t fit, but it might be that the horse has a forward girth groove. When a horse has a forward girth groove, it means that it’s forward of where, on most saddles, the girth fits, so a regular girth constantly drags the saddle forward.
The saddle-fitting site referenced above in a previous post has an explanation of girth grooves which is helpful:
