Yes, I've had problems with sizing also. The term 'duvet' refers to the comforter itself, and the 'duvet cover' is just that, the decorative protective cover. We've been using duvets inside a cover for about thirty years, so easy to wash the cover and keep the actual duvet clean. I've had great success with the quality of duvets and covers from a catalog called Company Store. They have many weights/fills of the duvets and price ranges to choose from. We use a lightweight cotton duvet cover for summer and an all-cotton brushed flannel duvet cover for winter. The flannel duvet cover came from another great catalog called Garnet Hill. Sadly though, even buying from the same source cannot guarantee the sizes will be the same. It's really ok to put a larger duvet inside a smaller cover as long as the difference is only a matter of a few inches. It just makes the duvet puffier and cozier on the bed. Just shake it around after you stuff it to make it even out as much as possible. If I was in the market today for a new duvet or cover, I would still purchase from those same two catalogs, Company Store or Garnet Hill. Sweet dreams....

I also have a king comforter in a queen duvet cover. My comforter is slightly bigger than the duvet cover, but doesn't cause a problem for me and fits much better than my queen comforter did. However, the best way to tell is to measure your duvet cover and then check the size of the comforter you order or buy. The actual measurements are usually listed along with the "king" or "queen" (at least when ordering online). That way you're not surprised. You'll find that sizes vary greatly--by as much as 8-10" on each side--while still being called "queen"!

I am dealing with this same problem right now. My comforter is 86 x 86. The Resto duvet I bought a few years ago is woefully large and it looks terrible. I know I should have at it with the sewing machine...someday. Looking around for a white duvet (which I think I want for staging my house) I notice that most are larger than the comforter itself. (Why can't there be a universal size for these things??) I spoke with Garnet Hill and their queen duvet is 84 x 84. Perfect! Rep explained that by being just a bit smaller, the comforter fills out the cover nicely and looks puffy. Now there is the issue of overhang. If I had to do it over again, I might get a King and have more coverage. But then it would be harder to stick my foot out the side to regulate my temperature at night! And the queen is probably easier to shake out while making the bed in the am.

The first and best thing to do would be to evaluate the actual condition of the comforter, and whether you like the way it fits your bed. If the comforter is in very good shape overall, and you have access of a sewing machine, the sky's the limit as far as finding a great fabrics to use to sew your own duvet. While I don't sew very often, if the comforter was in great condition, I think I'd give it a try. I can't imagine that a duvet would be too difficult to sew. If you don't want to get involved with doing button closure at the bottom of the duvet, you could always use velcro or some other method of fastening the bottom of the duvet. If you're questioning the condition of the current comforter at all, I would buy the correct size for your bed rather than using an ill-fitting duvet. If you go with another comforter, Personally, I've found that the box stitch, end to end down comforters to be the best overall down comforter. The down stays evenly distributed. That style has served all of our beds very well for years.