4'11" with a saggy 36D. I have seen most BRs go down two or more sizes. Is it possible to go down just one size, a 36C? (Photo)

Thanks for your inquiry. Yes, it is always possible to go down one cup size, but your surgery may then not always be covered by insurance. Your specific insurance likely has a required gram amount to remove per side in order for your surgery to be covered. It is always worthwhile to consider having a consultation with a surgeon to see if the amount required to be removed by insurance will bring you down only one cup size, otherwise you will likely have to consider paying out of pocket for your reduction.

I generally do not discuss cup size with patients, as cup
size means different things to every person. Rather, one of the goals of
surgery should be to remove as much breast tissue as possible to relieve your
symptoms while at the same time maintaining a size of your breasts that is
still proportionate to your body frame. A consultation with a board
certified plastic surgeon can help you to understand what your options are.
Best wishes.

It is difficult to predict exact cup size after breast reduction, because volume removed does not always predict the cup.

You have asked a very common question.  Insurance breast reductions are performed to alleviate the symptoms of having large breast, namely neck, back and shoulder pain, recalcitrant rashes, shoulder grooving from bra straps.  In order for insurance coverage to occur you must demonstrate the above symptoms, demonstrate a plan of care that hasn't worked ie pain medications, physical therapy, referral to spine surgeons or chiropractors etc.  After that your height and weight get plugged into a table called the Schnurr Scale which calculates your body surface area and then will give the amount of breast tissue that needs to be excised.  Most insurance companies adhere to this, while others such as Aetna require amounts usually 25% higher than the Schnurr scale.On the other hand you can have a cosmetic breast reduction in which your breasts would not be reduced by insurance criteria and then you can be any size you want to be.  The flipside is that you will have to pay for your surgery upfront.