So the cat wets the duvet.
I discover that there are such things as waterproof duvet protectors!
Argos has the cheapest one around at under £15, part of a bed set (mattress and pillow protectors included).
Here are a few facts about this product:
1) Yes, it is cheap so don't expect luxury
2) It is not breathable
3) It makes a crinkly, plasticky noise - luckily I'm a heavy sleeper.
3) It does the job and has saved my fluffy as a cloud duvet (the brand new one).
4) Because it is not breathable, it's very handy for cold winter nights.
My top tips for using this particular type of duvet protector:
1) Use 100% cotton duvet covers. They minimize the "crisp packet" effect by adding a touch of comfort/breathability
2) I found that if I don't zip the duvet protector up, the duvet itself does not slide or move down in a heap if trapped in the protector.
3) Use the buttons/zip of the duvet cover to hold everything together.
4) Have a shot of whiskey/brandy/liqueur before going to bed!
5) I've used the pillow protectors as bedding for the cat who eats, sleeps, wees - on my duvet
Cat has eaten, taken her medication and is now preening herself.