The biggest impact would be learning from a speech therapist about the techniques that suit my speech disfluencies and reading the book mentioned above. Even if you dont have access to a therapist, definitely read the above book. It's a quick read and written by fellow stutterers. I started meditation after those two events. For me it has been the final piece of the puzzle. Although I think meditation in the beginning would have helped me as well. Headspace is fine. For me, anything to do with mindful meditation seems to work. I prefer Jon Kabatt Zinn's videos and audio files. He has 4 45 minute audio files that I love. Try this https://www.youtube.com/watch?v=D5Fa50oj45s