When it comes to getting weights for home exercises for physical therapy we recommend starting with a pair of 5lb ankle weights (10lbs total) which are adjustable in 1/2 pound increments. Because many injuries involve small muscle groups this amount of resistance is usually adequate in the beginning. One can also avoid gripping which can be problematic for those with forearm injuries.
I prefer using the weights with leaded rods rather than those with sewn bags as the sewnbags often eventually break.
AllPro Adjustable Ankle Weights, 5lb pair