I had some lung trouble recently and I didn't like climbing lots of stairs. When exiting Bank on the Northern Line I used this route:

Go down the stairs fron the Northern Line to the DLR. There is a lift that will take you back up to the top of the stairs that lead from the Northern Line to the Northern/Central circulating area.

You can then take a lift to the ticket hall area. From there follow the signs for the Waterloo & City Line; but veer off alarmingly at the last minute and use the escalators (not weekends) that go up to Poultry.

Hopefully this might be useful to someone.