I am bothered by other dairy, I can’t have any yoghurt (commercial, didn’t try to make homemade yet) but I do well on homemade kefir fermented for at least 24 hours. I think that kefir grains feed on sugar. The way I understand it, if fermented right (at least 24 hours on temp above 70 degrees), there should be none or very little sugar left in kefir.
You can try to make kefir out of milk first, see if you can handle it. Since I can’t handle yoghurt but kefir doesn’t bother me, obviously they are very different. Also, on commercial products you can’t really trust what they put in there and how they ferment it. I think that according to protocol, kefir goes first and then Greek yoghurt comes after. I think that milk kefir gives you so much more than water kefir. It is filling so it helps with hunger, contains protein, potassium and many other great properties.