...he thought of having wasted tens of thousands of Dollars, and having to spend the time and money on replacing my wardrobe is an even bigger motivation than knowing I look good in the slimmer sizes.
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Love it - whatever works is good. And the slim you looks good.
My dad had two wardrobes (not really, but you'll understand), his "regular" clothes and his "fat" ones (his words). To be fair to him, he was a big guy - broad shoulders, big boned and 6'4" - who fluctuated from his "regular" weight of 215 - 220lbs up to 240lbs. He also said he'd never go higher as he wouldn't spend for a third wardrobe and, in truth, his "fat" wardrobe was made up of all old clothes as he never bought clothes when he yo-yo'd up to his heavy weight.
Since it's always about me: God forbid my 6'1" 150lbs, narrow shoulders, small-boned frame had inherited any of his bigger frame. That's what a 5'3" (she claims, but she's shorter) 100lb mother will do to a big man's gene pool. Heck, at least I got most of his height and her weight - think if it had gone the other way

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Within reason, the shoulders can be altered and trimmed down as well. It's not cheap, but it can be done.
This is true, but my experience is that the cost is very high when, many years ago, I looked into it. Also, I was warned that it takes a truly skilled tailor who can, basically, redo a lot of the upper part of the garment with real craftsmanship and experience.
I don't remember the price quotes anymore, but - at least in NYC - I remember thinking I could almost (not quite) buy a new OTR BB sport coat for about the same price as the alteration.
SG_67 knows more about this than I do, so I'm just adding my old impressions.