How small should I go? I’m 19, 240 lbs, 38K. (Photos)

The
technique I recommend is The Bellesoma Method. 
This technique 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, which allows you to
choose the size you desire.  Vertical
scars are avoided, nipple sensation and the ability to breast feed are maintained.Best Wishes,Gary Horndeski, M.D.

You seem to be a great candidate for a breast reduction, an in person consultation would be best for a detailed exam and evaluation.always see a board certified PS.

I would encourage you to consider getting another opinion if you were not comfortable with your first surgeons thoughts.  There are a lot of different techniques that can be done that preserve the nipple.  However, all large volume reductions have a chance of loss of sensation.  Many patients are still C to DD after reduction when they start with a large volume when an inferior pedicle technique is performed.  Also, some insurance companies may require more attempts at conservative measures such as physical therapy or weight loss before granting approval for surgery.   I usually recommend that patients are non smoking for 3 months and that they have their BMI at 35 or less to be the safest candidates for surgery with the lowest chances for complications such as loss of a nipple.  If you are not really convinced that now is the right time and it is not what you really want then I would consider waiting until you are really ready for surgery.  Best of luck on your journey.