If you go to an upholstery distributor, they will have different foam products, including memory foam, and may glue one up for you but it is a fairly easy DIY task. If you have to pay an upholsterer to make the mattress cover, the $200 Amazon deal mentioned above may be more cost effective. I bought some "close out" cover material at the distributor for $5/yd. The BIL, an upholsterer, made all new covers for all my foam cushions and mattresses.
An alternative would be to use a conventional mattress cover. We have some in the S&B that even have a pleated top, almost indestructible.