I'm on maternity leave at the moment, but normally this is my commute too. The strikes throw everything out the window, but on a regular day I found north dulwich to London Bridge then the jubilee line the easiest route because of having the fewest changes. Alternatively the bus (or walk) to Denmark hill. Via Denmark hill is actually quicker, however getting onto the tube at Canada Water is a nightmare. And my commmute was at a more flexible time.