I went searching old threads; seems to me RobiLee had posted about an awesome big bed she found. But I couldn't locate it.

I did find a post one person advised: take the sofa cushions from and old couch someone is throwing away. You can cover them, and they work well!

Or, you can make your own, Stace posted a hilarious thread here with instructions and photos:
http://petoftheday.com/talk/showthre...hlight=dog+bed