There are several benefits to being an American expat in London.
Some are practical (national health care), some will become clearer the longer you're here (earning your salary in GBP is awesome, the weather truly does suck), and some are superficial (Boots, the general social acceptance of being drunk by 6PM on a weekday).
Another benefit to living in London is having access to the high street glory that is COS.
You know the fancy section of H&M? Yes you do—it's the part of the store that's slightly minimalist, slightly more upscale, and has nicer fabrics. It's the part of the store that you never really shop from because it's too expensive and you're at H&M for Pete's sake.
If you took that and crossed it with Zara, you'd get COS (which is actually a part of H&M, for the record).
Sure, it's a little more expensive but the design sure is good and the quality is better. This is what COS stuff looks like:
A little taken aback by the Scandinavian minimalist approach? Don't be nervous! COS has stuff like this, too: