I definitely think that buckwheat is safer. I would do a week straight of buckwheat only and then a week straight of oat bran only. I’ve noticed my head gets a pressure symptom when I eat oat bran, I get some phlegm, and sometimes a cough.
The yeast can adapt to the foods you eat and so if you were to rotate to something else, it would adapt to this as well in time. In the long term, I wouldn’t necessarily cut out the problematic food items, I would just reduce.
I’d look into trying teff which is a prebiotic, tastes good, and is similar to wheat but no gluten.
Oat bran contains gluten and its not on bernie’s diet.