I’ve never had luck using coconut milk either. Plus it’s quite a bit more expensive. In terms of economy, unless organic milk is cheaper where you are, I’d say water kefir is a bit more economically feasible.
Also, a lot of people don’t realize that water kefir isn’t kefir at all. It’s proper name is tipicos and has no real relation to milk kefir. As such, they have different strains and different effects on digestion. Ideally, it be a good idea to work up to taking both regularly.
Kombucha is another powerful probiotic drink that a lot of people don’t take advantage of. Someone just told me that kombucha is a very strong chelator as well.