Proper leather shoes

The socks say 12 on the label and are usually the biggest on the rack. These are usually snug and ok on their own. Doubling up makes them a bit tight, obviously not much cop for insulating properties.

I too am often confused by the size labeling of socks but, in general, size 12 socks are not intended for size 12 feet.
According the table http://www.legsource.com/Hosiery_Consortium_Testing/shoe-size-vs-sock-size.html a size 12 sock is for a US men's 11 shoe which is roughly a UK size 10 (1/2 a size up and down will handle foot width needs).