London Temp Flat or Hotel recommendation

Hi, I spontaneously booked a flight to London next week from the 14th to the 18th. Well 18th not really, since we have to catch our easyjet flight early in the morning from Stansted.

I am now looking for a nice temporary flat or hotel to stay with my girlfriend. Since it has been quite a while I last visited London, I would like to ask you for recommendation where to stay and where to find an affordable (< 50€ per night) well connected flat or hotel.

In exchange I would be happy to share my flat or help with accomendation for your trip to Berlin.

Thanks for your help,
Marc