Your thinking behind about staying north of London would help. If it was to allow you to go north for some trips that is relevant as the rail network is constructed in such a way that you might have to travel south into London to then go North. Having a sense for how often you plan on going into London will help as some routes are much easier than others.
Placing you in a spot will easier with a sense for how much travelling you plan on whilst here?
Bit too broad a question. Do you mean you want to stay there the whole month? If so, you certainly want a small town that has shops, restaurants etc., and self-catering accommodation.
Are you here for work? Do you need to go into London every day (if so, where?)
I infer from your question you're looking for somewhere attractive, peaceful and generally unlike London, but you need to talk us through what you want before we can narrow down the hundreds of possibilities!Edited: 2:32 am, February 01, 2018
A couple to consider, Ely and Stamford. Ely has a direct train service into London, 1hr 15min, and is on the East West rail line Norwich - Peterborough, and services to Birmingham, including Leicester and Stansted. Stamford also lies on this East West line, London 1hr 45min via Peterborough..Peterborough is a major station on the London-North East & Scotland main line.
Otherwise just North of Greater London you might like to stay near Elstree & Borehamwood train station. Famous for its film studios and a lovely Jewish community. It still feels very much like part of London but without the London prices.
It depends if you want a “ little village “ or a town.
Little villages are unlikely to have rail stations.
Let us know a little bit more about what you are looking for so we could give better advice.
Revisting this question I concur with other posters above that this is too broad a question to answer in any sensible fashion. You will just get lists of English towns that individuals prefer. You need to provide more information about your reasoning and purpose of trip for us to help.