They've got to give us a solution for this in a patch, it's not acceptable the way it works now. I agree that athletic wear should be immune to temperature effects and swimwear immune to hot weather. That would solve everything about this it seems.
I'm so glad I read this thread before this happened to any of my sims. I play a rotational game, but have only played in spring and autumn thus far and not had much of extreme temperatures. I will definitely be on alert when summer and winter start in my two saves, and consider to give all my sims the ice proof and heat proof reward traits.
Lastly, I just want to add that I'm very happy we have these two death types. I'm pleased to have more randomness and consequences. But this is just bizarre and game breaking.