You have horses named Red and Poco and no western saddle? How is that possible?
A used western saddle is a great investment, IMO. Those bad boys will outlast an English saddle by decades.
In general, subtract one inch from the seat size you like in an English saddle to get your size in a Western saddle.
Otherwise, the discipline the saddle was built for will dictate the shape of the seat and placement of the stirrup bars. FYI, roping saddles will be Heavy.
Then look around for info on the approximate measurements of a semi-QH, QH and Full QH bars; through Arabian tree in there as well. Those widths are usually measured at the conchos in front that hold the skirt of the saddle to the tree, just below the swells. Western saddle makers have a richer vocabulary for the curves included in a tree. There is also a wider margin of error for fit in a Western saddle. I think you can be safe in choosing a tree that looks wide enough for your horses.
I like the show saddles made in the 1980s and 1990s. They are deep, well-balanced buckets. They are also pretty and no one cut costs on leather, silver or sheepskin as saddle makers do now. My MacPherson (an old, Los Angeles, CA maker) lets me ride as I would in a dressage saddle. In addition to a MacPherson, I’d buy an old Blue Ribbon, Broken Horn (still made in Baldwin Park, CA), or Circle Y.