People that get my blog know that I am a huge fan of facial fat grafting. I have even modified my cannulas to 1.2mm for even smaller fat. But this is the key for fat grafting-small product through little cannulas. This is ideal for the face. It is not appropriate for the breasts.
You are experience the loss of upper pole fullness. This is due to the stretching of the tissues, aging, breast feeding etc. If you want to replace that depression in the upper breast it is best done by doing an augmentation mastopexy. I would use a small, low profile implant placed under the muscle then do the Mastopexy. It is a proven procedure to correct your problem.
Fat grafting is always unpredictable. To fill your upper poles a significant amount of fat would be needed. I guarantee you that your surgeon will not be using 1.2mm cannulas to inject the fat-this would take many hours. Therefore, he'll put in as much in as he can and hope that enough will survive to correct the problem. Too many variable. You'll be left with lumpy, very asymmetric breasts. Don't do it.
If you don't want the implant that's fine. You can get the mastopexy done and if you're not happy with the upper pole depression you can always go back and get them at another time.