My son started doing the same thing at about the same age. So, we slowly weaned him off the swaddle. First, we left his feet undone, then one arm, then the other arm, and then we were done. I think if he is waking up in the night just to be reswaddled, then maybe he is ready to not be swaddled anymore. I was nervous about not swaddling because, like yours, my son seemed to startled himself. However, he has done great ever since. I let him still snuggle with his blanket and he likes that. Also, I started the weaning of the swaddle during the day at first, then when he got comfortable, I did that step at night and moved to the next step during the day. Good luck!