Have you had a professional bike fit?
You might find some solution to your pain and aero issues with short cranks. Shorter cranks let you put the saddle higher relative to the bars, giving you a flatter back, and also require a smaller range of motion at the hip. There are some very short options out there.
Look for a Retul fitter or medical bike fitter in your area. You may even be able to have the medical bike fit covered by insurance, I had that for a knee problem.