I'm male, 5'7" and about average weight (140lbs.) and would like a basic long double-breasted trench coat. Nothing too close-fit. I like room. What size should I be looking for? I have no idea what the specific numbers and letters mean. I was also looking for something like a Stafford brand. I'd go and try some on to see, but I'll be ordering something online for convenience. New to the whole 'clothes shopping' thing, as one can see.