Unfortunately there's a severe lack of good places that sell good fur in stores. Depending on where you live I'd just do a google search for fabric stores near you, but even where I live there's hardly any fur, much less good fur in stores, I've always ordered samples and my fur/pleather online.
People have made suits out of fleece before, you just need to be mindful of the pilling the fabric makes after being handled and such!
As for a dehumidifier, I'd personally recommend against that idea, you'd need a large enough area to help with airflow if I remember correctly, it'll add to the weight and bulk and if you need to drain it, you'll need to make an opening to take the dehumidifier out. It'd be a cool idea to try for sure! I personally wouldn't do it. I make vents in the ears and the back of the head, plus ventilation from the eyes and nose/mouth, and a lot of people put small computer fans in the muzzle and even the ears to help with airflow.