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)

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.