Hi... I live in a Northants village, and I've been a London commuter on and off for several years.
If you want this to work happily then I would really try to do as much homework as possible to understand the impact of the different commuting options. Commuting to some parts of London from here is a push, it has a certain detrimental impact on your life and relationships. I am often out of the house for 13-14 hours, but it's way way more draining than doing a 14 hour day in the local office.
I chose to stay down there a few nights a week in a 5 day a week room to take the pressure off for a while and it made a big difference to my stress level.
I used to live an equal journey time between Northampton & Wellingborough stations which are on different lines (into Euston / Kings Cross) but have always thought the service from Northampton is better. You nearly always get a seat on the way in and there are about 3 direct trains in the morning.
However, Northampton station is not great to get to as it's right in the centre of the (large) town through 30mph zones full of lights. My village is only 5 miles out but I would leave by 6.10am to hit the 6.42am fast train.
If you're working in the city, Bedford offers a direct service direct into Farringdon / Blackfriars which removes the worst part of the journey, which is the underground (it takes 10 minutes to get from your train to the underground platforms at Euston in the morning rush, and you may wait a couple of trains to get on). Therefore, for that particular commute, definitely worth considering.
If you just need to get to a major terminus then to be honest, Milton Keynes is a much much better commute than any station in Northamptonshire. The road links to the station are better as it's right by a main dual carriageway, it has more trains per hour, and the journey time on the train is 30 minutes a day less. Towcester +3 miles is worth a look if that appeals.
I would advise looking at some different locations and doing a "virtual commute" - i.e. use online resources to work out the realistic transfer time from the London station to the office, bearing in mind the peak of the rush can add +50% to this (the evening rush other than the really bad bits like navigating Bank at 5pm is often not so bad, maybe +20%), then work out which train to catch, and then check the drive time to the station from home +10 mins.
If you can't get it down to 4 hours a day door to door then it's probably not sustainable, in my experience. When you've narrowed it down, a week actually doing a couple of the commutes staying in an airBnB would be money and time well spent.
Lastly, if you seek tranquility, beware the north west ring road extension & associated housing development which has begun - map attached