Nicola...You might take a look at the SCD (Specific Carbohydrate Diet). Some on the Adult Metal forum are on this diet and it works for them. Their recipe for yogurt is the only yogurt that I can tolerate. Here is a little info that I found on the web. This diet allows me to broaden my choices of foods that otherwise cause me problems.

Yogurt made the SCD way has fermented longer than the standard yogurt, allowing the bacteria additional time to break down the lactose in the milk. This results in a yogurt that is easier to digest and absorb (simple carbs) in the small intestine thereby leaving less to cause trouble in the large intestine.

It seems that in many commercial yogurts additional milk solids are added as well as some of the SCD illegal ingredients. Commercial yogurts also ferment only for 8 to 12 hours. SCD yogurt is fermented for 24 hours.

http://www.scdiet.org/2recipes/indexa.html

Just an idea.