I'm a long time poucher (since 1996) and the best dietary change I ever made was to eat a 1/2 cup of cooked GF steel cut oatmeal every morning. It has to be the steel cut/unprocessed type of oatmeal and I make it with plain water.
The coarseness of the fiber seems to act as a "broom" sweeping everything out of me by the end of the day. I have not had any pouch issues since I began doing this a few years ago and am no longer on any meds or probiotics.
I don't know if this will work for you but it's easy and doesn't cost much so I thought I'd pass it along,
Good luck to you. Hope you find a solution.