Should I Choose High Profile Implants or Moderate+?

The more breast surgery I do the more I realize that there is no correlation between the size or model (profile) of implant used and resulting cup size.  This may have to do with several factors including: the amount of breast volume the patient starts with, the shape of the patient's chest wall (concave or convex), the type and model of breast implant selected (saline/silicone  and low/moderate/high profile), bra  manufacturer variance  in cup sizes, the  degree  of filling of the cup  with breast tissue,  and the subjective differences in patients perceptions of cup size. 
Much of the final “look” achieved after breast augmentation surgery  depends on several factors:

1. The initial shape, size (volume of breast tissue), symmetry of the patient's breasts. In general, the better the  preoperative breast appearance the more likely the breast augmentation “look” will be optimal.

2. The experience/skill level of the surgeon is important in determining the final outcome. For example, the accurate and gentle dissection of the breast implant pockets are critical in producing  long-term  well-placed breast implants. I personally think that these 2 factors are more important than any others, including type (saline or silicone)  or model (low/moderate/high profile)  of implant.

3. The type of implant used may  determine the final outcome, especially if the patient does not have significant covering breast or adipose tissue. For example, some surgeons feel that silicone implants have a more natural look and feel than saline implants because silicone gel has a texture that is similar to breast tissue. Each patient differs in the amount of breast tissue that they have.  If a patient has enough breast tissue to cover the implant, the final result will be similar when comparing saline implants versus silicone gel implants.  If a patient has very low body fat and/or very little breast tissue, the silicone gel implants may provide a more "natural" result.
On the other hand, saline implants have some advantages over silicone implants. Silicone implant ruptures are harder to detect. When saline implants rupture, they deflate and the results are seen almost immediately. When silicone implants rupture, the breast often looks and feels the same because the silicone gel may leak into surrounding areas of the breast without a visible difference.  Patients may need an MRI to diagnose a silicone gel rupture.   Saline implants are also less expensive than the silicone gel implants.
Other differences involve how the breast implants are filled. Saline implants are filled after they’re implanted, so saline implants require a smaller incision than prefilled silicone breast implants.
On May 10, 2000, the FDA granted approval of saline-filled breast implants manufactured by Mentor Corporation and McGhan Medical. To date, all other manufacturers’ saline-filled breast implants are considered investigational.
As of 2006, the FDA has approved the use of silicone gel implants manufactured by the Mentor Corporation and Allergan (formerly McGhan) for breast augmentation surgery for patients over the age of 22.

4. The size and model of breast implant used may  make a  significant difference in the final outcome. Therefore, it is very important to communicate your size goals with your surgeon.  In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or “C cup” or "fake looking" or "top heavy" means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.
I use  intraoperative sizers and place the patient in the upright position to evaluate breast size. Use of these sizers also allow me to select the breast implant profile (low, moderate, moderate plus, high-profile) that would most likely achieve the patient's goals. The patient's goal pictures are hanging on the wall, and allow for direct comparison.
I have found that this system is very helpful in improving the chances of achieving the patient's goals as consistently as possible.
By the way, the most common regret after this operation, is “I wish I was bigger”.

I hope this helps.

Best for you to spend most of your effort picking your plastic surgeon rather than your implant. It is very difficult to determine the exact size and shape implant you will require to best match your ideal breast image without an examination by a board certified plastic surgeon. Not just any board certified plastic surgeon, but one with many years of frequently performing breast augmentation surgery including different approaches, techniques and implant choices. This is because several measurements not to mention your breast characteristics are needed to determine the optimal implant size to obtain your goals. Without knowing these dimensions it would be difficult to make this determination. For example, the existing base width of your breast will determine, in many cases, the maximal volume per implant profile that you can accommodate. To illustrate; a 100 cc difference may make a significant difference with a narrow base width breast, but much less of a difference if you have a wide chest wall and wide breast “foot print”. Therefore, just because your friend may have a great result with let’s say a 350 cc implant to make her go from a “A” cup to a “C” cup size does not mean that you will have the same result with the same size implant. . Further simply placing implants in a bra to determine the size best for you is not always accurate as the bra often distorts the size, is dependent on the pressure the bra places plus the implant is outside your breast and not under it among other variables. Computer software morphing programs that automatically determine the best implant size can be helpful in some but not all cases (e.g. doesn’t work well in my experience with existing implants, sagging or asymmetric breasts). Using “want to be” photos however are useful if simply provided to the surgeon as I will further explain in the link below.

There is almost no difference. The difference in projection from a M+ to an HP in profile is millimeters. There is a bigger difference between MP and HP. Judging by the fact that you have almost no breast tissue and will thus be relying entirely on the implant for shape, I would suggest HP.