I recommend Geraldine's AirBnB, I stay at this AirBnB regularly when I'm in London for work. The transport links are very good to Southfields tube station, and Clapham junction train station. It's also close to Wimbeldon, with good bus connections. Geraldine is a very welcoming host, and the room is always clean and cosy. I have great nights sleep (this is very important to me, as I need to be well rested after flights/travel etc).