I wear midweight smartwool hiking socks year round. They breathe/wick really well. I have a pair or two of snowboarding socks, and even those I can wear in all but the hottest weather and still be warm in the winter.

The hiking socks have a band in them around the arch and fit very nicely. I have size 4/5 feet and buy the smalls. They fit snug with no rubbing, no extra sock, and no problems. Unless you really really like them tight I'd buy your size.