Can I still remain a 40D with a D implant to achieve a perky look, or do I need to be a 40DD? (photo)

Any breast implant that you chose will add volume and frankly will  "make you bigger".  So in a nutshell, if you simply add an implant of any modest size, you will be bigger.  I think what it sounds like you want is an improved shape, uplift to the breast, and upper pole fullness.  That would be best achieved in my opinion, utilizing a breast lift in conjunction with a modest silicone gel implant placed under the muscle.  I hope this helps.  Make sure to seek the advice and expertise of a board certified plastic surgeon.

Your photos are helpful. Although a full physical exam is
needed to get the best answer, I would suggest getting a breast lift to achieve
the look you want. Any implant will increase the size of your breasts, but
won't necessarily give you the desired results. If you're satisfied with the
size, a breast lift performed by an experienced, board-certified plastic
surgeon can give you perkier, more youthful looking breasts. Good luck!

Since
you are a 40 D and want to stay the same size, you do not need implants. You are an excellent candidate for a new
technique called The Ultimate Breast LiftTM. This technique reshapes your breast tissue
creating upper pole fullness, elevates them higher on the chest wall and more
medial to increase your cleavage. This
technique avoids the ugly vertical scars of the traditional technique,
maintains nipple sensation and the ability to breast feed. Best Wishes,Gary Horndeski, M.D.