Root vegetables, particularly 'old-fashioned' ones, like parsnips, swede/rutabaga, sweet potatoes, japanese daikon, etc

Bread that would meet the strict German legal requirements to be called bread

Brown rice over polished white rice, good quality basmati

Rolled oats

Maybe experiment with 'exotic' grains like quinoa, millet, buckwheat, etc

Avoid almost all noodles. High quality durum wheat pasta is ok. but measure it out, generally 80 -100g per adult.

Pulses such as lentils, chickpeas, etc

Green beans, peas, etc

Maybe you could also experiment with 16:8 fasting (each day only has an 8 hour window in which you eat), if you haven't tried already, to let your stomach properly 'clear' itself each day.

Hope this helps 👍