Help w/size of implants! 34D natural deflated post nursing. Suggested 300cc mod on my right and 375cc mod+ on my left side?

The fact that you have consulted the RealSelf group suggests that you are looking for some reassurance beyond your own plastic surgeon's recommendations. Needless to say, your plastic surgeon has the advantage of having evaluated you in person. Unfortunately the information you provided in your question is insufficient to properly advise you, and the "100 cc difference" is at best, your plastic surgeon's guess. It might also be a 50 cc difference or a 150 cc difference. The 300 Moderate Plus and 375 Moderate Plus may be just right, or not, and your plastic surgeon's judgement, experience, and inventory all matter. Expressing your desired cup size is notoriously inaccurate, and final breast size is the most common reason for patient disappointment after breast augmentation, either too big or not big enough. In your case, your asymmetry is what you presumably want to correct to the greatest extent possible.

As we think about breast implant size, Volume (300 versus 400), is far less significant than implant width and projection. Implant width is similar to shoe size. The implant literally needs to fit into your breast and chest. The volume and projection are what will determine the “look” you want, similar to the style or type of shoe you would select. It is true that for a given volume a high profile implant will have a narrower diameter, and it is also true that a person such as you with a petite frame will require a narrower diameter implant than a patient with a broader chest or larger frame. Other considerations such as saline versus silicone are also important, as are "round" versus "anatomical" or "form stable" or "shaped", smooth surface versus textured, and softer versus firmer with the different levels of gel cohesivity.

In my practice, besides a thorough interview process and physical examination with careful measurements, we use on lay sizers within an unpadded bra to help you understand what you are likely to look like in a bra, bathing suit, or T-shirt with a given size implant. In addition, and this is critical, we ask all of our patients to provide us with photos of their desired final look, with images of women’s breasts that most closely resemble the look they are trying to achieve. This serves as a visual guide that thankfully rarely leads us astray. This algorithm which we have been employing for over thirty years has proven to be very successful.

Make sure that you share with your plastic surgeon photographs of your "favorites" or ideal.
Best of luck to you.

You might want to consider how much bigger you wish to be. With 375 cc's you will gain two cups in size. You might find that is too heavy on your neck and shoulders. I would suggest asking to try on a variety of sizes to see what you like.

Thank you for your question and photographs.  I think you are starting from an excellent position and should anticipate a nice result.  Breast implant selection is an exciting, but stressful part of the breast augmentation process as there are so many choices. Unfortunately it is impossible to recommend the best implant style, size or shape without an in-person examination that allows for the measurement of key breast parameters, as well as permits an in-depth discussion as to your desired goals and outcome. I would recommend seeing additional board certified plastic surgeons to ensure that the implants you decide upon are the right ones to meet your expectations.  Several offices should allow you to "try on" several of the implants so that you can have a better visual representation as to what they would look like.  Best wishes!