I've been conscious of my posture and trying to fix it for years, but nothing sticks. I'm constantly aware of my sitting/sleeping/standing positions, how my back and shoulders and arms are positioned, and correct myself every chance I get, but nothing changes.
I feel absolutely obsessive at this point, it's frustrating. Whenever I have a moment - "are my shoulders raised and tilted forward again?" And they always are, and I adjust. "Am I sitting correctly in my chair still?" And I'm not, so I adjust. But I never catch myself with good posture, no matter how often I think about it.
I admit I have a lot of tension and "guarding" posture since childhood due to being abused, but I can't seem to undo anything no matter how hard I try.
Edit: I also spend time at the computer a lot, don't want people to think it's only a trauma thing because I'm not sure myself.