I have lived in a couple of places with significant Polish populations and both Tesco and Sainsburys have it in massive jars in their ‘specialist’ sections.
M did most of the legwork in researching it, but I reckon pick something you like (milk kefir might not be to your taste for example) and go with that. Sauerkraut is dead easy, but we’ve got fermenting jars do I don’t know if not having them makes it harder. The recipe o followed was in the Green Kitchen Stories book (might be on their site too idk)
Sourdough feels like a completely different beast and so low maintenance. I keep mine in the fridge, bake with it once a week/two weeks and never really feed it except as part of the building the leaven during baking.
Got 'er indoors the big Noma book last Christmas, and truthfully we haven’t done anything with it yet. It’s very science-heavy, lots of chat about microbes and getting pH levels right and that sort of thing, not just “bung some onions and some cider vinegar in a jar and wait for a bit” which is much more my level.
Have a whole shelf of stuff pickling in the fridge, mostly seems to be green tomatoes that didn’t turn because of the shitty summer atm.