Something to think about is that shorter isn't better with a western saddle. Almost all western saddle tree extend out on the loin. As long as they don't gouge into the horse at either end, that is OK.
A longer tree helps distribute weight over a larger area. Both my 15.2 purebred Arabian and our 3/4 Arabian "Appy" can handle a saddle that is 26.5 inches long with a rounded skirt. The larger horse could probably handle an even longer saddle, but both of my good western saddles are just under 27". They are both 16" saddles.
This is the smaller horse (14.3) without a saddle. His back is fairly short:
Both the white spots at his withers and the spur scars came with him, thanks to some idiot in Colorado. This was about a month after he arrived.
Here is my daughter using a Circle Y Mojave, 16" seat, 26.5" total length on him. My daughter's riding style drives me nuts, but Trooper worships her so it can't be all bad. The saddle pad is 30" long. Both horses have used that combo many times, and neither has ever seemed bothered by it.
I'd plan on getting a rounded skirt, and worry more about finding one the right width and with a curve that matches the horse than how long the saddle is. Good luck!