I am going to have to have a think about this one. My first thought was to make my western shirt in a traditional way, then with tassels and piping (very Rosemary Clooney) and then a plain one with embroidery or appliqué. But my second thought is do I want three western shirts....
There is a lot of potential in a basic shirt pattern - here is what I did with Vogue 8772. Seeing it might help you thinking
On the blouse I changed the neck hole into a V-neck to get the bow a bit away from the neck. Then I lengthened the original pattern into a shirt dress, and used the sleeves as a belt (sewn into the side seams). for the next dress I used the basic pattern of the shirt dress, changed the hem into a slanted one, cut the front on the fold and added neck hole and collar of Vogue 9112. So, I basically fitted one pattern once - it since became my TNT pattern for semi fitted dresses with shaping at the bust.