Because of Bay's huge wither and sway back, with his new saddle I had a custom pad made to fill the hollow so it would never bridge... that was my problem with the stuebben, it bridged and sored him at the back of the saddle. Bay's spine would hit between the pads on the stuebeen because of his build. He would get a huge blood blister there after untacking that would stand up as big as a half-racquetball.
To fit the new one, the saddle guy shaved and shaped a cashell foam pad to fit him... For ecurbh's new western saddle, he used a regular hair pad, and added panels of foam to it where needed. I am lucky to have our Dan the Saddle Man that owns the tack shop here. He comes to the house, no extra charge. Can't beat that.
(My horse's back is more swayed than yours! Nyah nyah! ;-) )