How Much and What Kind of Filler Needed to Improve Symmetry Following Accident? (Photo)

I am in my twenties and had an accident to the cheekbone which seems to have affected the fat distribution in the area (right as photograph). There is still fat but the cheek has flattened a bit..nerve damage maybe (I have episodes of neuralgia when a certain area of my cheek is stimulated). I am normally quite against tampering with the face in the twenties and had never planned to but I feel a SMALL amount maybe might improve matters. How much and what kind of filler could be used?