Library jobs are very hard to get now, I know a couple of trained librarians who can't get back in the field, one is a carer and does nights (LeQueen is another one on here).
It depends how much you need to earn, if you enjoy one-to-one teaching but hate the crowd control, and don't need to earn a fortune, tutoring might be a good initial way to downsize, esp, in London and depending on your subject area.
Fostering sounds like an amazingly caring job, but is it just your decision?- I think that's another dimension to considering what you would like to do, my husband would hate it.
If you are a good writer, what about getting out there and starting to write articles (on school-based stuff, or do you never want to think about that again?) However, I think you absolutely need to commit to that 100 percent and I'm not sure it is easy to make money, it could take years to build up a profile and you may end up writing stuff that isn't your dream, like webpage text (although nothing wrong with that). Textbook writing?