There are obviously a range of journey planners available nowadays, including Google and Apple Maps.
However, there is an excellent web site for planning any journey in the south-east: it includes trains (over-ground and under-ground), buses, coaches, and even walking and cycling.
It is very good at suggesting alternative means of travel, of which one was not aware.
It even has a text facility to get the times of the next public transport at a particular stop.
The link to this site is given below: