Diet - possibly very low carbohydrate.
That is, sugar in your tea is the least of your worries because it is usually only a small part of your daily glucose intake. Too much glucose in your blood is what diabetes is all about.
There is a LCHF forum with good reading here.
You don't say what your disability is.
If you have trouble walking then you might need to try upper body exercises using your arms.
A physiotherapist is the best person to advise on this and you should be able to self refer to get an appointment.
I haven't seen this recommended but I do note that in the London Marathon and the Paralympics there are some very fit people in wheelchairs so one option might be to exercise by wheeling yourself (using your hand to move the wheels) in a wheelchair to build up your arms and shoulders.
I have a book on chair Yoga which is full of exercises that you can do whilst sitting in a chair.
Just a few thoughts - someone with personal experience will no doubt be along soon.
Edit:
https://www.saga.co.uk/magazine/health-wellbeing/exercise-fitness/nine-easy-chair-exercises might be a start.