If your issues with strain are over, I'd say just slowly add fruits like you said. Try the peeled apples out, then wait and see how you react to them. If you're fine, then add them to your diet slowly. Then try something else. It's a slow game of learning what your j-pouch likes and doesn't like. As time goes on, you'll find your j-pouch to be less finicky then at the beginning, and usually able to tolerate any normal diet. If you can handle light fiber like from the apple, then lettuce shouldn't be too far away from your future...just make sure you chew it very well!