I too have had back surgery (disc removed).
For me a Russell Day Long (great folks to work with) & Heli Bars seem to have worked on my "B". RDL with risers & pull backs, worked on 2 other bikes.
If you have the OEM Honda seat, you wouldn't be with out a seat.
I had raise foot pegs that made my hips hurt, went back to OEM.
I've never used a Mustang, they are great looking seats.
Ever use a "bone cracker"? After trying 6 or 7, I found a good one that helped me a lot....... Then I moved