Some breast starting points are better than others
I will apologize in advance for this, but you do not have a starting point for a home-run result. Your breasts will never have the separation you want and your tissues look to have poor tone and are droopy off the implants you have despite a lift. You already look huge for a 5'2" patient and 550HP will only accentuate this.
It's obviously your choice, but in my opinion, for a much better looking breast, you need to not go larger with the implant but you do need to complete the lift to a full anchor lift becasue you still have excess lower pole skin (horizontal skin laxity). This will get your areolas level since they currently are not and it will give you better projection and less bagginess in the lower pole.
Achieving a "fake" look with breast augmentation or enlargement with implants
I agree with many of my colleagues in the comment that you have significant quantities of natural breast tissue that you must "overcome" in order to achieve the look you desire. It is my impression, as others have stated, that you consider a revision mastopexy with partial reduction and limitation of your implant to a 350cc high profile in order to actually achieve a decrease in breast diameter (and wider cleavage) while accomplishing an increase in projection.
Breast Implants vs. Mastopexy for athletic body type
For the look you are desiring, I feel that another mastopexy is your best option. The circum-periolar-vertical lift that you already had can be repeated to lift the breast and provide more of the round look. Larger implants can also be used if you desire, but I also believe you will need a capsule plication (or inframammary fold reconstruction) to raise the position of the implant. This is not the easiest case to make look the way I think you want and I would make sure that your surgeon has experience with such.
Increase in breast implant size and profile
From a purely technical point of view going from a 350 cc mod plus to a 550 cc high profile will definitely give you more projection and a rounder look. You must realize that the base size of the 550 cc is actually larger than the 350 cc moderate plus profile so there will not be any more separation between the breasts. It will also make you very large considering the look you currently have and the fact that you are 5'2".
Two principles in breast shaping
Dear Ms. S.
The key to great breast shape depends on
1) the starting shape of your breast
2) the type of Implant
From your photo it looks like you have had prior breast surgery and that there is a slight difference in the size of your breasts.
In order for the best result, you may consider re- lifting your breasts and making them a little more symmetrical.
The implant can then be chosen on the restultant breast shape from the lift- it could be a moderate plus or a high profile implant and the size can be determined by trying on sizers.
The more breast surgery I do the more I realize that there is no correlation between the size of implant 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 (saiine/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.
It will be 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" 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 press 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”.
Achieving a "fake" or very round look
I have developed a procedure that would be appropriate for you. I call it a "reductive augmentation". Actually, I remove breast tissue from the lower pole of the breast, place an ultra high profile implant, and complete your mastopexy. I have been able to achieve a very round result in most patients.
High profile Breast Implants for athetic build?
From your photos it looks to me like you need a lift of your existing breast tissue and you might have capsular contracture on the right. I think your size is too big right now and would recommend against 550cc. The problem with chasing upper pole fullness is that the result will be temporary.
Hold the silicone implant in your hand horizontally and then vertically; the gel flows. It will flow to the bottom of the implant. Initially, when the implant is placed, the tighter skin in the bottom of your breast will force the gel up, creating a rounded look in the upper pole.
Over time, the skin in the lower half of your breast will relax and the gel will be more in the lower half of your breast; ie you will lose upper pole fullness and your breast will sag even more. I would not advise 550HP for you, especially with your height of 5'2".
You would also benefit from a revision of the lift, focusing on repositioning your breast tissue higher and creating a narrower breast base.
Going larger with HP implants wil probably give you more projection but they will be heavier than your other implants, and may make you sag quicker than the lighter ones. You will have an initial fuller appearance up top, but eventually they will come down a bit as well.