There was a Dutch (I think) fursuiter who came up with a unique cooling vest for use under the costume to prevent overheating. It was so effective & good, it ended up getting adopted for military use!

Here’s an article about it: https://www.thedailybeast.com/how-a-cooling-vest-invented-by-a-furry-made-its-way-into-the-us-military

I believe it’s called the EZ Cooling Cooldown Vest, but it may have changed names or rebranded or something.

My idea: specifically make one for use in bras.