Bluewater - no one has yet answered you about lightest weight etc coat, and I am not an expert either -- but if I were you, thinking of buying one coat to have on hand for winter travel, I think I'd get hold of a LandsEnd catalog, and look in there for something like a "long stadium coat."

The catalog is full of educational stuff about what various coats protect you from. I think the long stadium thing has the advantage of looking a bit more urban than a jacket & covering more of you.

LL Bean might have something too. But warm-light-urban isn't that easy a bill to fill, I find. (Live in cold city, NY. Sheepskin, leather, fur, fake fur -- warm but heavy. Wool is heavy too. Down can look "wrong" to me here.)