I would suggest actually physical exercise - training in the gym or calisthenics. I achieved my own "worry-free" stutter & improving my body image, improved my stutter more than anything else. I currently don't rely on any speech techniques & I just go about my day. I still stutter mind you, but it is almost non-existent & I don't mind it. But the other thing that helped me was - reading aloud at home daily (2-3 pages of a book) & doing mock presentations at home(before the real presentation at school). P.S. I would love to chat with anyone about improving their own speech (I went through the same hard path as you, and I know how you feel). I accomplished it quite young also - at 18 years old. DM me freely! Have a great day everyone!