Random thought, but the firmness might be the result of capsular contracture.
You could try doing implant massage. One variation on this theme would be to rest your body on your breasts on a firm surface (eg, on the floor, not on a bed) and slowly/gradually maneuver your body to and fro, thus creating a fairly constant pressure on the implants, but varying the directions slightly as you do so. I would think 5 mins every morning and 5 mins every evening would be plenty.
If rolling around on your boobs like this is painful (inside the breast somewhere, not painful to other parts of your body), that could be a clear sign of having capsular contracture. If this is the case, it might be worth having a consult with your surgeon to confirm/refute.