Hi RebeccaMI, Yes you can definately ride him in a Western saddle, infact a Western saddle is the best choice. (You’re right, there are so many terms and opinions on western saddles it can be super confusing, especially to an english rider!)...so here's the main thing I explain to my clients that I think will help you understand a little more about these type of saddles. Western Saddles have much wider bars (the weight bearing part of the saddle tree) than an english style saddle, this means they have more surface area so distribute the saddle and riders weight over a greater area on your horses back and are easier on the horse despite the extra weight of the saddle itself.
Don’t panic too much about saddle fit…yes it is important but let me break it down a bit..there is no such thing as a perfectly fitting saddle, your horses conformation will change throughout its whole life due to amount of exercise, nutrition, the season etc. So don’t stress yourself out trying to find the ‘perfectly fitting saddle’.
I’ve been sent many wither templates from drawings on paper to bent pieces of wire but custom making a saddle from this alone only causes mistakes. I always like to fit the saddle on the client’s horse with my own eyes and make sure they understand the points they must check to make sure it’s fitting properly.
1. Bars- they should be in even contact with your horses back in order to distribute the weight evenly
2. Channel- ensure this is not putting pressure on your horses spine
3. Gullet- make sure this high enough and wide enough so it’s not putting pressure on the wither of your horse
4. Position- the saddle needs to be placed in the correct position on your horses back so it doesn’t restrict his shoulder movement
From your photos and what you’ve described the first type of saddle I’d try on him would be a Western with Semi QH bars which should give you some more room for his higher wither depending on the type of saddle tree that was used to make the saddle.
Also, regarding the correction pad you have that still didn't seem to fit the problem, I have many questions from clients on this topic, there are so many choices it makes your head spin. Saddle pads can help correct MINOR saddle fit issues, they help me adjust one type of saddle to fit many clients horses of the same physical type however, no matter what claims they make I believe they CANNOT make a poorly made or fitting saddle fit your horse. If you have a quality, well built Western saddle and a variety of quality saddle pads that are not too thick and cool, cushion and absorb moisture you’ll be on the right track. It you could find a saddlemaker in your area I’m sure they’d be happy to explain some options to you and even help you fit your boy with the correct saddle. :)