Years ago, I was a distributor for Covercraft. Great covers and good people to work with. Not sure if Beverly Hills covers are sold by Beverly Hills Motoring Accessories, but if they are, another good choice. Covercraft makes covers for everyone and will custom make one to the size you choose. They have patterns for a bazillion different covers.
Pick a material for your intended use. My Avanti has worn the same Beverly Hills cover for almost 40 years. Soft cotton, custom fit, sits in a covered garage, so it's mostly a dust cover. My 914-6 has a Covercraft poly cotton cover cover that keeps bird crap off the paint and will let moisture out if caught in the rain. It also sits in the garage most of the time and has had the same cover for about 25 years. I've used Covercraft poly cotton covers on a Porsche 944 and a Mustang GT 2+2 - both were "outside" cars. The covers lasted about four to five years under the desert 120º sun, all weather, strong winds, and the occasional sand storms. You'll need to wash the ouside uded cover from time to time to remove airborne grit that can scratch paint.
Dennis