No implants here as I am comfortable with what is now a B cup but I have a suggestion. Buy a bag of rice and some nylon hose. Measure out the rice and place it in the bra to try out different sizes.
One thing to consider is that your choice of bras will be limited in the larger sizes and they are less attractive than bras made for smaller sizes. The additional weight will also require wider pads to keep the straps from cutting into your shoulder. If these are tradeoffs you are willing to live with, go for it.