Another London Holiday Help Request!

[mattyn1]

With work commitments and a family member ill health our planned driving holiday to Bordeaux has had to be shelved, so we are now looking at London again for about 5 to six days in August.
We (2 adults, 3 kids age 15, 11, 5) enjoy Chessington, Legoland and of course stuff in London, and have stayed previously at the Holiday Inn in Sutton, which is ideal for the attractions and the City. However it appears booked, so am looking for recommendations of places to stay, that won't cost the earth! We are looking at going post Olympics - so anything from 14th August ish.
Also, would prefer a pool (kids love swimming), you get the idea!

Thanks all in advance.