It is actually not that difficult. If you reach the South Circular Road, A205(fairly clearly signed as such), don't cross it. You can drive on it, the extended ULEZ will reach the inside Kerb of the South and North Circulars.
In any case, you have a bit of time to research a strategy, and decide what to do. ULEZ extension starts in August 2021, I think.
The problem I have, which is the main reason I am changing cars, is that my parents actually live inside the zone, and when I need to go there, there is nowhere to park except round their house, due to CPZs.
So if I want to leave the car there for a few days, I will end up paying several lots of the £12.50 daily charge.