My personal theory is that many of the problems stem from homogenisation. Youngsters' guts are not designed to handle these teeny particles. So it could be worth a try with unhomogenised, chemical free cows' milk. Especially unhomogenised, chemical free, AA Jersey cows' milk

. (And note that many Crohns disease sufferers find that raw, unhomogenised cows ' milk isn't just tolerated, it actually helps them.)
if so, you could look into Smiling Tree Farm in Shropshire. They supply raw, unhomogenised Pasture for Life Jersey milk by post. Expensive per litre compared to homogenised shop milk, but cheaper than running your own animals, especially for just one! (And pain free too.) Christine Page is very approachable if you wanted to discuss it with her.