Good Breast Size After Reduction for Large Frame?

It is difficult to determine exactly what size you will be after a breast reduction and there are other factors that may play into this decision.
These include your health and smoking history.
Furthermore, larger reductions have a higher risk of effecting the nerve and blood supply to the nipple and areola.
It is important that you have a full discussion with your surgeon to understand all of these issues when planning your breast reduction.
In regards to the sagging, almost all reductions involve achieve some degree of lifting. More significant sagging (ptosis) will generally require larger and longer incisions.

There is no " ideal” breast size. It is very important to communicate YOUR size goals with your surgeon.  In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or “C cup” or "fake looking" means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate. The patient's goal pictures are hanging on the wall, and allow for direct comparison.
I have found that this system is very helpful in improving the chances of achieving the patient's goals as consistently as possible.

I hope this helps.

A breast reduction is exactly what you're looking for! It's difficult to guarantee a cup size after a reduction, but it gives your surgeon an idea of how small you'd like to be. Also, a reduction lifts the nipple and areola. So, the sagginess that you're concerned about will be fixed as well.