I'm going with white potato's also at the moment. I know they are nightshades but they are apparently easier to digest than sweet potato's. White rice is even easier to digest although the blood Sugar rollercoaster would be too strong for me personally, even with protein and fat.
I'm relying on stimulant laxatives at the moment, mainly cascara sagrada. I'm aware of the long term dangers. Got some enzymes to try as well and will try some high dose magnesium although it could cause some mineral imbalance.
My constipation got so bad that food was not actually passing into my intestines and it felt like it was still in my stomach for my next meal. I took some betaine HCL after the meal and could feel it burning up my throat! Has left me with some left side abdominal ache.