In reply to Toby_W:
My top tip is to buy shirts from a proper shirt company - TM lewin, charles tyrwhitt etc
I have mostly CT shirts, they come in a collar size, arm length and chest fit. They're not expensive and often have offers (say around £20 each). I'm 16.5 inch collar, super slim fit chest with 36 inch sleeve. No normal high street retailer offers anything like that
It's a real shame outdoor manufacturers don't do something similar. I end up buying stuff from certain places as I know they'll often fit well (scandinavian brands, plus rab and montane for top half, UA for base layers etc)