I need help choosing an implant size would 350 or 375cc be too big for me? (Photos)

Thanks for your question, & including your photos, they really help! Based upon your photos and my experience of doing thousands of breast augmentation surgeries, I’d say that you’re an excellent candidate for breast augmentation! I’d advise you to try on sizers: they really help in determining what volume that you want. I’ve found them to be invaluable in my own breast practice, & have a very low revision rate because of it. I also think 375cc range would look great on you. Best of luck to you!

Patients often think in terms of cup size when considering augmentation. Unfortunately, devices are sized in terms of milliliters (cc) of volume. This can lead to some confusion when sizing. Additionally, it is important to remember that cup size itself is not standardized with variations from one manufacturer to another. Unfortunately, as many women can attest their cup size in an industry leader such as VS is not necessarily transferable to another brand.
Another point which is often under appreciated is that of anatomy and starting point. Any implant will add volume to the volume which is already present. The implant is additive. A particular volume will not necessarily confer the same cup size to different patients (often times it will not even confer the same cup size to different breasts in the same individual...remember they are "sisters" not "twins"). 
A general rule of thumb is that 125cc can represent somewhere between 1/2 to a full cup size increase. Smaller volume differentials (25-50cc) are typically less consequential representing a volume change of less than a shot glass. However, I have found these numbers, at least anecdotally, to be of little help. Patients often present with notions/goals which do not correlate with these sorts of sterile volumetric assessments.
When sizing patients, there are a number of useful tools including:
-3D imaging (has the added benefit of offering a volumetric analysis of the pre-operative breast)
-Breast sizers (rice bags)
-Goal photos
I also recommend that patients commit to a particular look rather than a cup size. Once a patient settles on a look that pleases them the overall cup size increase becomes less relevant.The key to obtaining a natural result is to stay within the parameters defined by your BWD. This will ensure that you avoid the dreaded "fake" look. 
With regards to your specific question, it is difficult to offer definitive advice without an in-person exam. The best advice is to "love the look" not the cup. Find a look that you are happy with (which falls within your BWD). If you are seeking greater volume go up in profile. This will offer a more dramatic look with greater volume for a given breast width. I would not struggle over 25 cc as this represents a subtle difference (5 teaspoons or less than half a shot glass).
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

The best cosmetic result in any particular breast
augmentation patient depends on a variety of factors, including: Your
individual anatomy, desired outcome, realistic expectations, a thorough
discussion with the plastic surgeon about the options, and an understanding of
the pros and cons of any particular implant choice. Proper sizing is not just
about the number of cc’s. or the type or shape of implant. The thickness of
your tissue, breast dimensions which include the width, height, and projection,
as well as chest wall width all need to be considered when choosing an implant.
Trying on implant “sizers” of various shapes and volumes while wearing a tight
t-shirt, bra, or bathing suit at a preoperative visit will help you and your
surgeon choose the optimal implant.There is very little difference in the appearance between a 350 cc and 375 cc implant once it is placed into the breast.

Keep in mind that following the advice from a surgeon on
this or any other website who proposes to tell you what to do without examining
you, physically feeling the tissue, assessing your desired outcome, taking a
full medical history, and discussing the pros and cons of each operative
procedure would not be in your best interest. I would suggest you find a plastic
surgeon certified by the American Board of Plastic Surgery and ideally a member
of the American Society for Aesthetic Plastic Surgery (ASAPS) that you trust
and are comfortable with. You should discuss your concerns with that surgeon in
person.

Robert Singer, MD FACS

La Jolla, California