Small Frame with Silicone High Profile 275cc, 280cc, 300cc?

Your question reflects "size anxiety" that is unjustified by your situation.  You will have an excellent result if you find a good surgeon.  Your body will not look heavy because of your skin situation and nulligravid status with a low breast surface to volume ratio.  Breast implant dimensions are more important than volume.  Based on your photos and expressed desire, you will be pleased with a mid range or high profile implant that matches your pre-existing breast base width.  It's a matter of personal taste which you prefer.  A mid-range profile will look very nice and natural, sexy in swimsuit or snugly fitting tops.  A high profile will get more attention, and present a more obviously augmented look on your very delicate frame.

You need to try all of these sizes on in a bra in your surgeons office before you pick.  I would not go off pictures of other patients because differences in height, weight, chest circumference, etc will make the same breast implant size look very different on two different women.  Good luck.