We have cheapy sheepskin covers in our car.
Get them from supercheap when they're on sale.
Use for 5-10 years.
Throw in washing machine when covered in mud/sand.
Throw away when completely wrecked and buy a new set.
They're not as tough as the canvas ones, but I like them because they're soft. I don't find them hot at all, the exact opposite in fact.
Father-in-law has cheapy canvas covers from SuperCheap on his ute, and loves them. I do find them a bit burney when you jump in, and they're about as comfortable as sitting on a piece of canvas could be. That said, the vinyl seats aren't great to start with, and these do a really good job of protecting the seats from dirt, water and crap. He's had them on for a couple of years now, and they still look like new.
All that said, I believe there is a fair bit of difference between the cheapy canvas covers and the good ones.
Good luck!
Matto