Do you think that because you are tall you maybe hunched up a bit when you were younger and more self conscious?
Pretend there's a wire in the top of your head pulling you upright (like a puppet)
Tell everyone to 'correct' you when you slouch.
(Reminds me of a funny line from a Barry Manilow book. He was supporting Joan Rivers, the audience were a bit meh. Ms Rivers got a bit fed up being ignored and shouted at a girl "Don't slouch Honey, your tits'll sag" )
Easy. You need Lucy clayton school of deportment in Gloucester road. Same school Joanna Lumley graduated from. I went in 90s. Think they do short day courses. My nan sent me for my 15th birthday. For 6 wks. Kid you not.
Can still switch it on if necessary but less useful now a sahm.... Lol