What's the name for the style of shirt that's associated with Western wear, has two breast pockets with flaps, detailed stitching, and generally pearl or imitation-pearl buttons or snaps?

I'm finding it impossible to shop for these because I've only ever bought them in thrift stores and don't know what they're properly called.

Edit: Not looking for flannel or denim, but lighterweight fabric, something I'd wear under a jacket not instead of one.