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Wow. You sound like you are in excellent shape. Not very fashion, but I think going to a series of the main high st shirt makers and trying them out is your best bet. We're quite lucky in London, because there's far more choice than just Brooks Bros. One of them will do a slim fit that's the slimist. They also have a wider range of neck and sleeve sizes. If at that point something still needs taking in then buy a bulk of the closest and get them altered.
(In case people don't have twitter https://nitter.poast.org/dieworkwear/status/1630357679326793729#m)
As in the slimist of the main shirt makers are still too loose?
The TML "Fitted" seems pretty slim to me.
What happens if you have to sit down?