I don't see any health issues that you should be concerned with if you undergo a breast augmentation while having only one kidney. Your nephrologist and/or urologist may recommend that you not use NSAIDs such as Advil after the kidney donation, but there are other pain medications that you could use after breast augmentation that would be fine. By the way, fantastic to hear that you are donating a kidney! One of the most wonderful gifts you could give someone!
As long as you are healed and everything is functioning well, then there is usually no issue in these cases. Your surgeon may want to get clearance from your nephrologist prior to surgery.