I had a similar problem with my dog when he was young.
As it's so difficult to clean a duvet - I remember trying to cram one in the washing machine - perhaps you could invest in some blankets/ throws or even a plastic sheet to put on the bed during the day. The plastic really works as they can't snuggle up on it, and it doesn't hold smells. The wee does run off it sometimes though, I warn you! You can get them for children's beds to go under the sheet, or even a plastic dust sheet from a DIY shop wold do it. Not pretty, but during the day it doesn't matter really and it's better than cleaning your bedding every night before you can get in it.
Hope this helps.

Laura
i had this problem with my 5 month old rescue dog if she got frighthed shed go in to the bedroom and pee 0n the bed but as she got less nervous she stropped doing this.