No problem. No point in your making the same mistakes I did 20 years ago! :-D
In OK you probably don't have as much English riding gear hanging around, but there MUST be a consignment store somewhere near you (all that used stuff has to go SOMEwhere!)
And, happy 50th! I just turned 49 in March, my hubby passed that big milestone 3 years ago . . . You're right, 50 does deserve something special.
Do you have a trainer or a tack repairman you can get a second opinion on a used saddle from? Just make sure the saddle tree is not cracked or split - everything else can be repaired.
Hair, Stuebbens seem to be made for the more cobby and straight-backed type of horse. My mare is a very up-and-down build with very prominent withers, and the Siegried galls her withers. My Courbette has a cutback pommel and I use an oversize rectangular dressage pad with a liftback insert. That fits her very well, but when I show her in hunter and use a sheepskin, I have to make sure I pull the pad up into the throat of the saddle or she'll get a gall. Even her New Zealand rug wears her hair away at the withers (even with sheepskin on the edge).
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.