DD1 has been going through a fairly defiant stage too but not the hitting part (maybe its a boy thing?) so I've been sending her to sit on her bed, and then after a few minutes going in to talk to her and see if there's something wrong, or if she's just being a monster. Can you give your son a firm cuddle to stop him from hitting you, but to gently put him in time out?

Sorry lovely. No real advice I know. I hope its a stage that passes quickly