Of course I looked up knitting patterns for sauna hats after I read about them. (Who doesn’t?!) There were far less than I thought there would be but Ravelry had a handful, including this felted gem with jaunty earflaps!
The designer’s Ravelry page tells me I can get the pattern in English, which is good because their actual site is all in Norweigian. It’s still fun to click around, though–and look at what else I found I could make for a future sauna life: A DRINK-HOLDING MITTEN! 
Those clever Norwegians…