As well as what has been mentioned so far you might like to consider The Pilot Centre at Denham. It's a 30 minute train from Marylebone followed by a 20 minute walk. No commercial training there though. I was very happy with my PPL there.
Personally I found public transport a bit awkward with Stapleford so bought a cheap car. From what I remember the bus from Romford is only once an hour and doesn't run on Sundays. I didn't know there was a bus from Theydon Bois - this may well be more convenient.
Also, I know that this topic has come a few times so do a search for lots more info.
Here is a start.