Would a breast reduction from 32D to a 32C/B be helpful for exercising pain?

You are an optimal candidate for breast reduction surgery if your breast size is disproportionately large compared to the rest of your body frame and causing your back and shoulder pain. The surgery will also help to reshape and recontour your breasts. Very large breasts have the natural tendency to sag or hang low, so breast reduction surgery will lift them up and help them look perkier under tight clothing.
If the size of your breasts is preventing you from what you want to do, it is not unreasonable to have the procedure done.  Consult either virtually or in-office with a board certified plastic surgeon who is an expert in breast reduction surgery so that you can discuss your ultimate goals, BR pros and cons, the best time to have the surgery, and whether your medical insurance is likely to pay for it. With most modern techniques of breast reduction, the ducts should be preserved as well as the sensation. Therefore, breast-feeding should be possible.

Unfortunately, you have not provided photographs.  However, the technique I recommend is The Bellesoma Method.  This will reduce and reshape your breast tissue creating upper pole fullness without implants, elevate them higher on the chest wall and more medial to increase your cleavage.  The weight of the breast is transferred to the underlying pectoralis major muscle resulting in pain relief without excessive reduction.  Vertical scars are avoided, nipple sensation (in 95%) and the ability to breast feed are maintained.  Best Wishes,Gary Horndeski, M.D.

Thanks for your question!  One of the main reasons breast reduction surgeries are performed is to relieve discomfort.  A breast reduction will absolutely help with pain during exercise.  It sounds like you will be a great candidate!  Be sure to consult with a board-certified plastic surgeon.  Good luck!