There are a huge choice of hotels, guest houses, B&B’s, and self-catering apartments in London, as you can see from this map:
In the age of TripAdvisor, there is probably little point recommending individual hotels here as the information will be easy for you to find yourself online.
The only thing to be wary of is a small number of hotels that offer rooms which seem remarkably cheap until you realise that the bathroom is down the corridor and shared with other people. If a hotel room seems very cheap, just double check that it includes a “private bathroom”.
It’s also worth bearing in mind how you will be travelling to the meeting venue. Either choose accommodation that is walking distance from the venue, or check the Underground and Bus maps to ensure that you can travel easily from where you choose to stay.