Definitely do some research. I have a (twin) down comforter that I got for college that I still have, and it is my favorite blanket in the whole house. It lives on the sofa for TV snuggling. OTOH, I've been through 2-3 other down comforters that are crap (but cost more).
One thing to watch for - if they advertise that it "allows the down to shift," run screaming in the other direction as fast as you can. What they really mean is "eventually, unless you adjust the blanket daily, you'll end up with a ton of down over your feet and the equivalent of 2 sheets over your shoulders, which will be freezing."
The best thing is *true* "baffle box" construction. In that case, the quilting is completely enclosed around each "box," and there is a piece of fabric stitched in there to give it some height (the "baffles" - that way the down can expand and you don't get thinner areas along the stitching.
Next best thing is regular true "box" construction. Same as above, but without the baffles.
What you do NOT want is for the down to be able to move from one square to another. This is shockingly hard to find (at least it was the last time I shopped for a down comforter, which was several years ago).
Finally, look carefully at sizes. When I was looking at king duvets and duvet covers a few months ago, the actual measurements would vary by as much as 10". I would have been peeved to buy a 92" comforter with a 102" duvet (or vice versa), even though they were both "king."
For more information, check Google.
Re: **6** re: down comforters
I just a friendly gal looking for options.