Your shoes will make little or no difference to the impact. When you calculate the numbers you will see why. Running puts a tremendous stress on your body and at nearly 20st that is all the more relevant. I'd recommend mixing your running with some cycling and or swimming for some lower impact training.
As said above I recommend a walk run program. Keep your calories in check. Running is great exercise, but people have a tendency to reward themselves with treats that undo all the good work and then some on top. It is really hard to run from a bad diet.
Get some advice on running technique. Try not to stretch your legs out too far in front of you, your feet should land below your knees. Anything in front of that is putting extreme force through your knees and hips and is actually slowing you down.
Enjoy the progress you make, but take it slow. Pushing it too hard will lead to injury and that can be devastating when you are making good progress. Remember slow and steady progress is the best way forward.
Good luck buddy, I was 17 and a half stone at one point, now happily at 13st 6, I've been there and done it. The sacrifice is worth it!
You seem to be running at a reasonable level and I imagine that means you are covering a lot of miles. Some of this injury could be as simple as too many miles without the necessary base fitness behind it. Only you will know if you have been pushing that too far though.
For me personally I think structured support shoes are a nightmare for most runners. I think they encourage the foot into an unnatural shape and position and keep it there throughout a run when a foot should be able to turn and mould itself to the run, it should be the point of contact that fires all the other muscles off in your legs and right up to your core. A support shoe stops lots of this happening.
For me a neutral shoe is the right shoe for most people, I mean the name even suggests it. If you have been running for a long time, your body should be able to cope with you feet having a bit more freedom!
As for the shoes, well you just need to try a load on. Personally I'd stay away from anything Nike. The people in their shops have no clue about how any of their shoes work or who they are supposed to be for and having tried to talk to Nike about it, I feel like most of the company doesn't have a clue either! To me they entice you in with good (fashion) design, but the substance isn't there behind it.
I'd do a load of research, then wait for a sale while you recover then go and try a load on and see how you get on.
It is a massive pain to get rid of and because of the type of tissue it is it doesn't heal well.
The give away with PF in terms of diagnosis will be that it hurts like hell first thing in the morning and at the beginning of a run, it will slowly diminish on a run or when you walk and then return with a vengeance after rest or the next day.
There are a few things you can do to deal with it in my experience.
- Stop running until it goes away - Sports orthotics might help to support the arch and allow it to heal (It worked for me) - Put up with the pain using massage and pain killers. Although be aware if you are running long distances and using anti-inflammatories your stomach will hate you and it could damage your kidneys. Gels are therefore preferable.