My boyfriends horse has odd shaped withers. The saddle we were using doesnt fit...just noticed (feel really bad

) it is pinching his withers and making him soar and swollen. We have been riding bare back for about a month. The swelling has gone down but he is still soar. None of the saddles in the barn fit him. His spine stands out and his withers are just boney and wierd. Any help. I attached a picture. But its hard to see what I mean. Thanks