Proper leather shoes

I'm a NA 10.5 and now will no longer buy anything other than XL in socks, virtually every brand seems to have shrunk their sizing in the last years.
(I buy at least 70% wool, usually merino)

With House of Cheviot XL would be too large. With my size 12 (13 US) I get a perfect fit with Large (UK 10.5-12.5). Their XL is intended for UK 13-14.5 (EU 49-50.5). For a US 10.5 I'd expect you to get a good fit with their Medium.
Corgi used to make very good socks--- they used to be a main supplier of tartan hose for the Army---- but I'm unsure of their current range. I mention them as their sizing was different.