replacing booster/ adjustable car seat cover

Ok, big question.  My son has a Britax Frontier- the original one.  The fabric Britax used stinks- it's a mesh that is all shot after less than 2 years.  And of course they just changed the design of the car seat, so now I can't even really buy a replacement (we have the red, and my son said no way does he want the brown, the only one they still have- which is mesh anyway so same problem).  What I really need is to replace the cover.  Yes, I know, some folks are making them on Etsy, but they're all using regular cotton fabrics or minky- neither of which is going to last with a 4 year old boy any better than the original did.  I'm thinking of a few options, but what I really want is our old Cowmooflage cover from when he was a baby in the Britax Marathon- that fabric was totally indestructable!  Any ideas where I can buy that fabric?  Thoughts?  Yes, I also know that doing something to the cover voids the warranty, etc.  I just want to put it over the current padded cover- our warranty isn't being helped by the Britax cover falling to pieces!  I'm even thinking about buying a Marathon cover and cutting it up using my Frontier cover as a pattern!  Any thoughts, ideas, suggestions?

I've never tried making a car seat cover just because it seems you'd have to get the fit just right in order for the cover to stay in place with all the use it gets. I've always wondered how long it took those Etsy sellers to get their pattern just right.
Wasn't the Cowmooflage cover made of a minky-type fabric? I seem to remember that these were made with microfiber. This is probably why these stood up so well.
If you're willing to try and copy your cover and it will just be going over your current cover, then I would try to find some microfiber. (I just typed it into Google and got a half dozen sources.)
Also, you'd probably be better off starting from scratch rather than buying a Marathon cover and trying to make it fit. Just a thought...