E.B.
No advice or insight on the colectomy, but we have family members with UC and Crohn's, and my daughter has a form of gastroparesis with complete pelvic floor muscle malfunction.
We've researched the impact of foods and eating habits, and I wonder if in addition to your gastroenterologist, you have consulted a nutritionist? We have learned that carageenan, guar gums, xanthan gums, and artificial sweeteners (anything ending in -itol, processed stevia and agave nectars, Splenda, Equal, etc) can be extremely harmful and/or irritating to some people with digestive disorders. Carageenan seems to be in everything these days, and it's amazing how many products have guar and xanthan gums in them. We avoid all those processed foods. (And yes, the Stevia and agave nectars that are commercially available on the grocery store shelves are not natural; the pure stevia plant itself is natural, but the common brand name varieties of the extract are highly processed.) By eliminating all those foods from the diets of the people in our family affected by digestive disorders, we have been able to get some relief.
Also, my daughter is instructed by her doctor to eat a low-residue diet. That means removing all peels from fruits and vegetables, cooking fruits and vegetables well, avoiding seeds and nuts, avoiding high fiber foods, etc, and that has helped a lot. There are lots of resources for low-residue diets online.
I'm not sure if this applies to you, but if it helps, then, that's good.