MCH, please don't be annoyed with me if you have already tried this and it didn't work, but are you taking Metamucil (psyllium husk fibre)?
Without it, my j-pouch would have been miserable. I found it cushioned my BMs, neutralised the stomach acid, and (somewhat) reduced the sprinkler effect by creating a sort of gel around whatever I had eaten. (I took a heaped teaspoon of the fine powder version in minimal water, gulped down quickly, immediately before eating.)
I dread summer with numerous BMs, cos it's impossible to keep your nether regions clean. How many times I have wished for a bidet! My best holiday ever was in Japan, where almost every toilet has an inbuilt bidet. It was heaven.