DD reacted to the baby yoghurt like Petit Miam as most have added fruit which always includes some kind of preservative. I got referred to Jalna range from this site, thank god !!! Its about the most tree hugging hippy yoghurt you can find, tastes good too (I eat it now too).
You can try dairy such as yoghurt, custard, cheese from 6 months. Introduce cows milk in things like cereal from about 9 months and then finally, cows milk as a drink from 12 months. The big no no is using it as a replacement for breast/formula before 12 months (although I did it from 11 months - lol). If you have any family history of reaction to dairy then you may want to hold of introducing dairy. Well worth a chat with your CHN, GP or Ped (when ever you happen to see them next).
The good thing about trying some-thing like yoghurt or custard from around 6 months (in small proportions) is that you can test for any reaction. It will gradually build your babies tollerance to dairy (unless alergic of course) - including allowing their digestive system to adjust to processing it. It is also a nice tasty treat which most bubs enjoy.
I recently tried frozen yoghurt on DD - she loved it. The key is to look at the ingredients. Initially its best to stay away from any-thing with added sugars, preservatives, artificial sweetners etc. Best of luck, hope your bub doesn't spew much cause yoghurt is probably the worst smelling baby spew EVER - lol.
DD is 3yr 8 months - DS is 6 months