Would the location of the Staybridge Vauxhall work for you? I want to say the couch folds out into a bed in the one bedroom suite, and if the child is on a different sleep schedule than the parents, there's something to be said for being able to have the lights on in one room but not the other.
The Staybridges offer large rooms by European standards, generally a reasonable price (breakfast included) by London standards, and can be a good option if the location works and you're okay with a lighter housekeeping schedule.