Always bringing the knowledge to the Food Board! I love your posts. I'm still contemplating the cooked shrimp question. ( other thread)
As for the onions, I get that same sensation, and it's getting worse as I age. Used to be that only raw whites and yellows would cause this, so I tried to stick to the purples(reds). Now, I get the sour mouth and acid burning with them as well.
The saute'd options are a fine suggestion, but the dried and reconstituted method may be worth a shot!