You say you like your size but you want to be "just a bit fuller." Breast implants will increase your size, give uplift, and make you "fuller on top", roughly in proportion to how large an implant you choose. You would have to be very significantly larger to improve all three things. I'm not sure what you mean when you say you "want to keep the "flip" under the breast" so make sure you and your plastic surgeon understand what you mean by that. As far as "working out" and your "fear of loosing my breast" is concerned, you need to clarify that as well. It sounds like you want to work out but you are concerned about the effect on your breasts. You can expect more sag in the future, but you can have some control over this by keeping your weight stable and avoiding exercises that stretch the skin and ligaments supporting the breast. Best of luck modeling Bikinis.
You have a lot of company from many other women when you say you want to have breasts that don't sag as much but at the same time you "do not want to go big". The cause of the sag is that you have more skin than is necessary for the current size of your breasts. To correct this you can reduce the amount of skin (That's what an uplift does) or you can increase the size of the breasts with augmentation. The larger the implant you choose the more uplift you get. Your problem is you don't want to go too big, and you're the only one who can say what's "Too Big" for you. If you want the maximum uplift without going "Too Big" I suggest you choose the largest implant that you feel you will not feel is "Too Big" for you, and that's the best size to give you the most uplift without going too big. Best of luck to you.
Surely you don't mean to ask will you weight gain change the appearance of the implants, but rather don't you mean to ask about the appearance of your breasts? The implants will not change their size with your weight gain or loss, but the size of your breasts in front of the implants will likely change with weight gain or loss. Breasts contain both glandular and fatty tissue in different proportions and these proportions you likely inherit. The fatty tissue is the main tissue that gets larger with weight gain, and smaller with weight loss, while the breast glandular tissue usually changes with hormonal influences. You can get some idea of how much of your breast is composed of fatty tissue by how much your breasts have changed in the past with a weight gain or loss of 10-15lbs. The more they've changed=more fatty tissue, while little change in the breast with weight change=little fatty tissue and more glandular tissue. I hope this answers you question about weight gain and change in breast size and I hope that was your question. As far as your question about will this make "them appear more taught/round/fake?" or not, every one will have a different opinion about how different sizes and shapes of breasts will appear, but the only one that should really matter to you is your own opinion, you shouldn't expect to change what opinions other people will have. I hope this helps you with your questions and gives you some things to think about. Best wishes to you.
The cause of capsular contracture has yet to be proven. No one knows for sure why some capsules contract and become a problem. It's not uncommon to see a contracture on one breast and a normal capsule on the other. The cause and the best treatment are not always known and may be different for individual patients. If you have a breast augmentation that's one of the risks you have to accept. Every surgery has some unavoidable risks as does life.
Just from the appearance of the photos, it appears your left nipple is a little lower than the right and the left breast may be just a little larger. You can perhaps verify if this is true or not by how your breasts fill out each side of you current bras. My best guess is that 550cc implants are likely to raise you about 2 cup sizes if you stay with the same number bra you are currently wearing. Have you tried on a bra you want to wear after surgery with the 550cc implant in the bra in front of your breasts? If you haven't I suggest you do so to get an idea of the increase in size and weight that it will add. If the left breast is larger you may want to add a few cc. or ml. to the right side to get better balance. You should get significant uplift with that size implant. As the years go by, you surely will see more sag. Your expectations will determine if that's OK with you or if you want to try to make changes. So many things in your future can make big changes to your breasts, you will have to wait to see if you want an uplift later or not. Good luck.