Most bakeries use commercial yeast in addition to starter in what they call sourdough. If you haven't already been doing this, you need to ask if there's commercial yeast in their sourdough. You might need to shop around to find a bakery that does it pure.

My partner has a similar condition (not celiac, not gluten sensitive, but 'something in bread' sensitive) and she found that sourdough from locally made starter was way easier on her system than anything from bakeries or the store.

(Source: We've been experimenting with breadmaking at home, so I've learned more than I ever expected to about bread over the past year.)