Liz not sure if you remember but DS was definitely this sensitive. I had kept him gluten free as well, which included oats. When I decided at 9-10 months to try oats we went with ReadyBrek, which is totally milk free but made in a factory with milk products (or something along this line...it's a "may contain traces of" situation iykwim) and the result was unreal. At first I felt it confirmed that I was right to keep him gluten free and that at 9 months old he was presenting celiac symptoms because it was THAT bad. Mucous and blood in stool, screeeeeeeeeeeeeeaming fits, thrashing around, arching and doubling over in pain....it was like his newborn days all over again, but worse.
Trying to recall my exact line of thinking at the time, but for some reason, we tried oats shortly after....I think I wanted confirmation, possibly
but went with just a plain old bag of Irish Oats. And waited, and waited. Nothing. Tried a couple of days in a row, no problems at all. Couple of weeks later, tried the readybrek again thinking that it must have been some random gastro-bug, but with the readybrek got the same reaction again. The ONLY thing that I could put it down to was that there was some ridiculously miniature trace of milk in the readybrek and it was causing THAT bad of a reaction in him.
When I first trialled soy with him, he had about half of a small pot of soy yogurt and he vomited projectile, for hours.
I guess in one way it was good because I knew that when I did a milk trial at 15 months and he was fine, I really did know that he was fine, kwim?
Lots of hugs as I can't imagine what you are going through with the elimination diet xxx