I can give you some suggestions. First, you should not pick a round frame reading glasses, which will make your face look more round. Second, you can choose the style of frame which trailing is slightly higher. Third, the feet of the frame should be a little thin, so ad not to make your face have an enlargement effect.
If you have a big heads, you must choose reading glasses with big frames that fit for your head so as to give you comfortable wearing. As for the shape of the eyeglasses frames, which is no business with the big head. You need try on and find the best looking frame that can flatter your face and fit for your personal style.