My DS is also off the chart, Let the airline know before you go. If you haven't booked your ticket yet, let them know during booking. If you did book already call and ask them to note it. When you check your luggage in let them know at that time, also.
With SWA they will give a peanut dust folder to bring to the plane, and we give that to the attendant at the door of the plane and another one on the plane.
If you don't warn them before the plane is loaded with snacks there wont be anything they can do. SWA will load peanut free snacks with enough warning before boarding.
I also was told to give my DS Benadryl before boarding. I will also wipe the seat, arm rest, tray, window, seat belt and my seat before he sits, then I drape it with a blanket for him to sit on. He has been flying since he was 2 and now is 11yrs. it is scary but doable.
After an announcement one time a gentleman sitting next to me and my DS open a snack bar. I politely asked him if it had peanuts in it, because we were the ones with the allergy. He apologized, he just wasn't thinking and he put it away in the over head bin. I thanked him with gratitude and told him I was really scared because my DH wasn't with me and flying with a n allergy child is so scary. He understood, his son had allergies. Hopefully, you won't have any problems and you will have caring people on your flight the way we did