You have given a fair amount of information about your previous surgeries, and you now have more experience than most patients with saline vs. silicone, above the muscle vs. below the muscle, and augmentation only vs. lift plus implants. Certainly childbearing and possibly breast-feeding can have substantial impact on a woman's breasts, whether they are previously augmented or not. Your surgeon's solution was to do a lift, and switch from submuscular saline to submammary silicone. I might have disagreed with this choice just on the basis of the description alone, and apparently your result bears out my reservations about this plan.
Now, however, either you or your surgeon is suggesting "gummy bear" implants. The "true" gummy bear implants are not yet FDA-approved for general use, and I believe the study (involving only a certain number of plastic surgeons) has been closed to further enrollment. These study implants are form-stable, cohesive, firm, textured, teardrop-shaped implants that require a larger incision (not a problem for you with lift scars), do not move with changes in a patient's position, are position-sensitive (they have to be gotten in exactly the right orientation in the body as the texture prevents any movement--if they are "off" then they stay in that asymmetrical out-of-position orientation), and they remain teardrop-shaped when reclining, which normal breasts do not do (they flatten to a round shape and slide laterally towards the side of the chest). Thus these so-called "anatomic" gummy-bear implants are not really anatomic at all. Oh, did I mention that they cost more as well? Perhaps you can tell I was not a big fan. Nothing wrong with the implants, or the surgeons that used them, just overall I felt these implants were a suboptimal solution for problems that rarely exist. I certainly would not oppose using them in certain select patients in a "salvage" situation where nothing else has worked, but for general augmentation, and even most re-do patients, smooth, round, 5th generation cohesive silicone gel implants (Memory Gel by Mentor, or Natrelle by McGhan, then Inamed, now Allergan) are state-of-the-art implants that provide superior results in most patients.
Since these latest implants are also cohesive (more cross-linking between the silicone polymer molecules), and cannot leak or rupture, many patients incorrectly call them "gummy bear" implants. Both types of implant are cohesive, but with different levels of cross-linking, different degrees of firmness (or softness), and shape (round vs. teardrop-shaped), and surface (smooth vs. textured). These are NOT the same, and yet the cohesiveness is the biggest advantage of the present 5th generation of silicone gel implants in use. Read the link below for more information I have included on our website.
I would suggest several opinions from other ABPS-certified plastic surgeons in your area, particularly those with extensive breast surgery experience. Switching pockets again has a whole set of concerns that did not exist when going from submuscular to submammary, and this may not be a good idea. If you want larger implants again, you may need the additional tissue coverage that returning to the submuscular pocket would allow. But then what does your surgeon do with the "old" submammary pocket? As I hope you can see, perhaps a dose of wisdom combined with a kettle of experience is needed for the best outcome. Perhaps your own surgeon can provide this--if so, please still get several other opinions; your surgeon's judgment and sage advice will clearly shine through compared to your other bits of input. But after two operations so far, let's get this one right, shall we? Good luck and best wishes!