What about living on the DLR?
Is the DLR accessible for people with mobility impairments?Yes. The DLR network was the first fully accessible railway in the UK and provides step-free entrance and exits to all stations and trains, making journeys much easier for people using wheelchairs, with prams or carrying heavy bags.
There's some nice places on the DLR, it's much cheaper to live out east as well.
Might be worth checking with abellio and confirming your son's chair is acceptable and then you can tell the driver that when you get on. According to tfl - Most wheelchairs, including motorised types, will fit onto buses but motorised scooters with handlebars can't be carried onto buses.
So as long as it isn't that type you should be fine, maybe print out the page?
I have some medical equipment which is allowed to be used in flight but flight attendant's knowledge is patchy and I have had it taken off me before, so I eneded up getting a note just to stop it being such a hassle every time.
Have you read through everything on the tfl site? You'll probably get a lot of answers there, sounds like more research is needed.
http://www.tfl.gov.uk/gettingaround/transportaccessibility/1167.aspxIf you need a one off trip, sounds like you can do this for free -
http://www.tfl.gov.uk/gettingaround/3222.aspx