As @MakkaPakka says, Uniqlo sizing is pretty unreliable. I'd say the sizing of their regular collection was pretty standard. I'm a size 10 and I'd take a small in Uniqlo for a regular sort of fit. The sizing of their collaborations, however, always seems to run very large - I take an XS or XXS.
Depending on your style, the Uniqlo men's collection may be worth a look. I've bought jumpers and trousers from the men's collection and if I were taller (I'm just over 5ft) I'd definitely look at the men's coats and jackets.
I'd say Cos sizing was pretty standard although the clothes are often designed to have an oversize fit.
