I will second the flannel sheets. I don't have them, but climbed into bed at my grandmother's house while visiting a few weeks ago, and AH, BLISS. I told her in the morning that I spent a good 5 minutes just rolling around in bed before falling asleep, the sheets were just exquisitly cozy. And she promised to pick me up a set when she goes back down to Florida for the winter (yay grandma!)
I agree that beds/bedding are super important, because we spend so much time in them. I have a wonderful, king sized mattress. Only because I'm lucky enough to have in-laws that - through their impulse buying - end up passing a lot of barely used stuff down to us. This mattress is probably my favorite possession. It's so comfortable. I spent a lifetime on hand-me-down, 20+ year old, falling apart mattresses. I honestly thought I was an insomniac until I got this mattress. For the first time in my ENTIRE LIFE, I fall asleep when I lay down to go to bed. I don't toss and turn for 5-6 hours any longer. It's just awesome.
As for bedding, we use a down duvet, and have two very good quality pillows (again, always had cruddy old pillows growing up, so this is just divine - got them as a wedding gift and I love them). What we DON'T have is decorative throws, pillows, or anything of that sort. While I think they can make the bed look very inviting and cozy, they really don't serve a purpose and go against my "decluttering" ideals. I plan on making a really great duvet cover, though, and a matching bedskirt if I'm able to afford some fabric after Christmas.
Will be watching this thread for ideas.