Pretty difficult to get lost - if heading from Southampton up the east coast just keep the sea on your right, turn 'left' at the top and again keep the sea on your right, when you get to the other corner, turn left again, keeping the sea on your right all the way down to Lands end, continue turning to the left and go along the South coast keeping the sea on your right until you get to Southampton, then you will know where you are.
If doing it the other way, reverse the options and keep the sea on your left.
In all seriousness - whilst I have only walked parts of a few coastal paths they are generally well used and well marked, I would guess that it will be mostly the same except (maybe) in the very wilds of Scotland and possibly parts of Wales.
Get a GPS loaded up with OS mapping at 1:25,000 (it will clearly show all of the footpaths and routes) and you cannot (famous last words) go wrong.
You would need (maybe) a couple of hundred OS 1:25000 maps, at £10 a time that's a lot of money.
You can actually programme the co-ordinates for every Lifeboat station and it will give you course, distance and ETA. In an emergency (you slip and break a leg or wotever) you have your position to tell the rescue services.
You are planning on 'sofa-surfing', B&B ing etc so recharging the batteries would not be a problem.