Roly also had a tough time as a pup trying to find a food to suit him - try to keep it simple, stay away from any processed treats, pigs ears (or any ears) gave Roly the runs (he has only ever had one). Fish is a good route, but I have to admit I think scrambled egg is very good for firming up things (no milk or butter though) with boiled rice for a few days (nothing else). Then if stools are looking a bit better start to add some fish (only very small amounts) and gradually start to substitute the egg. If all goes well for a few more days then start to add in some kibble, only a few pieces at first.
The first kibble that worked for Roly was the JWB puppy fish & Rice, but then when we switched to the adult variety it started all over again. Surprisingly Chudleys worked quite well for him, but eventually we switched to Arden Grange Lamb & Rice and that suits him very well along with being part raw fed in the evenings.
It is a fine art and thankfully Roly is not as sensitive as he used to be, though there are still some things that will upset his digestion and he can only have them in small quantities.