Symprove. It is expensive, but it is one of the few probiotics which has been proven to real the gut intact. I can honestly say it has proved life changing for me.
Sometimes you would need to eat a ton of sauerkraut in order to get enough probiotics, plus homemade is better than shop bought (which is often pasteurised in order to sell it, which kills off the good bacteria), and some people just don't have the time to make it.
Home made sauerkraut is supposed to be one of the best but any fermented food will help. I’ve found kefir in the international food section on Morrison’s to be ok but kombucha is not for me.