The bridge of my nose is a bit high. If I have it lowerd, can bone be used for grafts in my nose?

No. Fat grafting will make the bridge of your nose even higher. If on the other hand you have a hump and the valleys in between can be filled to straighten the nose, you should use fillers, not fat since fat simply does not last on the nasal bridge. Radiesse, Restylane (dermal fillers) and the like would be a much better choice. Good luck from nyc.
Rhinoplasty. The bridge of the nose can be lowered during cosmetic nose surgery (rhinoplasty). Occasionally grafts will have to be placed in the nose to fix structural issues, however these are most often cartilage from the septum (most common), ear, or rib (least common). Less commonly bone is used for very specific purposes.
Slow down! Sounds as if you've not only determined your cosmetic concern, but also the solution! the latter is something an abps-certified plastic surgeon spent years of training and experience learning! you owe it to yourself to obtain one or more consultations, describe your concerns and goals, and the listen to the proposed solutions, then ask questions! this approach will lead to the best outcome!