Thank you for your question, measurements and the photo.
Sizing is best done in person in the plastic surgeon's office with his or her highly skilled staff. Different ways to size are using the Mentor Volume Sizing System, 3D imaging/simulation, and New You Visualizer. Less sophisticated but very effective ways are placing breast implants inside a bra and filling ziplock bags with dry rice to "stuff" your bra. All of these will give you a reasonable approximation to help you choose the right implant size
275-300 mL moderate plus implants will probably give you a solid C cup, but this is only a guess-timate based on one photo. Individual results do vary. Again, getting sized in person is important.
As far as achieving a natural look, tear drop anatomical gummy bear implants can give you the size you want and still look natural. The gentle slope at the top of anatomical gives a natural look without that high, rounded implanted look from high profile round implants.
To be sure what is right for you, see two or more board-certified plastic surgeons in your area to make sure that you are healthy and a good candidate for surgery. Before your visit, make sure that your surgeon is skilled and experienced using all varieties of breast implants.