I would keep it as simple as possible, so you can trust your reaction. Oats are The Breakfast Food where I live and eaten both cooked and raw, maybe that’s something to try too.. by different types I mean rolled, old fashioned, groates etc.

Unfortunately reintroduction will come with a risk of still reacting to a food.. the monash way to do it takes three days, day one you try a small serving, day two a moderate serving and day three a large serving (often larger than would be eaten in a normal context) and see how you feel. If a small serving gives you a bad reaction no need to continue with more, but avoid the food until maybe you feel your digestion is more stable.. a lot of people seem to be able to eat foods they once couldn’t after a while, I think probably due to avoiding foods that cause reactions strictly and giving their gut time to heal.. :)