Looking for weight management/sensitive stomach food recs

My dog (3 year old Pittie/Beagle/Lab mix) is just slightly overweight, even though we get regular exercise, his human cousins drop food a lot as they are toddlers and he is a snack fiend. He also is consistently eating grass when outside and sometimes having reflux in the morning.

Looking for a food to calm the stomach and provide the nutrients to stop the grass, and other extra curricular, eating and also act as a bit of a weight management. (although heavier on the digestive sensitivity though, I know the food scraps don't help)