Train,
What a pickle you are in..I assume the best thing for you to do is to control the hives, so it doesn't flare up your asthma. Gotcha!
If heat makes your body break out..I would think you need to wear breathable, loose, lightweight clothing...so your body temps do not rise.
I have known children that could hardly take showers, for the water brought on hives.
Hope you find a solution to your problem.
Peace out,
janet