Last year, we invested in a futon dryer (futon kansouki) which is essentially used on those days when you can’t air the futon, dry out shoes and boots, and even dry your clothes.
We also used it to heat up our futon before going to bed. We have a wool-like fluffy mat under our sheet, a top sheet, then another futon. As it gets colder, we add a blanket or two to the mix. We would heat up the futon for about 10 minutes, then get in. I rarely suffered from sinus problems and sore throats, last year. So, the couple of yen we spend to heat up the futon every night helps me save on doctor and pharmaceutical bills.
I had a look on Rakuten the other day and the cheapest ones go for around 4.500 yen. There might be other bargains out there. Well worth the investment.
Recommended by GB on the Frugal Japan mailing list.