One thing won't work and that is any kind of appliance supposedly to correct slouching shoulders. At sixty three and with one nasty climbing fall from my twenties the fifty two years of malnutrition prior to diagnosis and of course my radio opaque lungs, has left me a little (too) stooped. Yet another clue of my undiagnosed CF, Kyphosis was attributed to my heritage. In a twisted way my doctor was spot on, just the wrong chromosome.
A birthday gift of three Rolfing sessions in my 20's turned me on to a physical therapist trained in slipping people back into their membranes. Although Rolfing is mostly breaking up mesentery adhesions and slipping these interior membranes that hold our lungs and guts in place as well as every muscle, tendon, nerve and vein throughout the body, back where they are supposed to be. Trust me they are not where they belong.
If you have ever prepared chicken, you’ve seen mesentery membranes between the skin and meat, wrapping each muscle like a special sheath. Mesenteries wrap around every muscle in your body with a lot of mass in the back because there are so many muscles. Every injury, infection or whatever causes scarring in muscle, bone, tendon and of course mesenteries that develop adhesions. For a short time, maybe three months, I had to wear Large dress shirts as my shoulders were now tight in my regular clothing. It isn't a panacea but if improving your posture is the goal, consider it as one of several things that will help reach your goal.
LL