There a few ways, for once clothes as you mentioned already. Not just clothes some accecories and hats also can greatly improve heat or cold resistance as well.
Going into it in salamander form also gives extra heat resistance and this resistance can even be upgraded in the dojo for salamamder.
There is also the varia field item in town which when used reduces heat and cold dmg temporary.
As for starting the card collection quest, there is an angel in the heavenly plains who loves card collecting, speaking with him will inatiate the quest.
Also just saw that i forgot to remove the unfinished text from the volcano quest, no worries that quest is finished, will fix that.
I hope this helps!