Not a silly question at all. I use Flannel / Cotton only, also, I buy mine one size bigger then it say's. Better fit over the car. Since you don't have to worry about rain or wind in the garage, one size larger fit's over the car down to the floor, without touching the floor. I found a 61 Vette is the correct size for the Cobra, for my Mazda Rx-7 I use a 2004-5 Ford GT cover. I use this company, very easy to deal with, and knows their product's.
https://www.carcoversdirect.com/