I had a great stay at Helen's! The apartment is lovely, and exactly as it is in pictures. It's in a really convenient spot, perfect for walking and with easy trains into London and (though I didn't take any) buses leaving from just across the road. Yes it is on the main road but I'm a very light sleeper and the window was still enough to block out the worst of the noise.
Helen was a great host and I'd definitely stay at her place again. Thanks for everything, Helen!