Hi Shell, what a shame you're having to sell a bike you love in all aspects apart from the physical impact. Bad luck about the GSX that you liked too.
I ride a CBF1000 & wondered if you've considered it. It's a bit of a dark horse and not well written about. The engine, a detuned fireblade has ample power when needed but happy to bumble along too.
The seat height is adjustable. I'm 5ƈ with a 29" inside leg & am fine with it on the lowest setting and standard suspension.
Seating position is fairly upright so perhaps that would help your back problem.