In reply to Removed UserBoi Bangor:
Call me a pessimist, but I suspect anything you stick to it will be peeling right off again sooner than later. I don't think you'll manage a lasting repair that doesn't involve some sewing.
And denim does sound like a bad idea tbh, you probably want something waterproof and harder wearing than that. Maybe something like this: https://www.pennineoutdoor.co.uk/fabrics/Waterproof-Fabrics-MEDIUM-AND-HEAV...
Could you cannibalise a broken camping chair, a rucksack or something? If you keep your eyes open perhaps the Cosmic Supply Company will deliver something suitable to a skip near you.
If sewing means paying someone else to do it for you, I guess the question is how much life is left in the foam and is it worth it? Assuming the foam is still good maybe you could try advertising on here to see if anyone has the same model with knackered foam and a decent cover that they'll sell you cheap. Never know your luck.
Post edited at 20:23