WM has good reputation and their bags have a good resale value. If you are set on a quilt you may be able to sell your WM Ultralight and buy a quilt of similar warm without having to lay out too much (if any) extra cash.
On the other hand, if you are not sure if a quilts is for you or you want to preserve the resale value of your WM Ultralight, maybe just roll tightly (and clamp down) the hood and then you can open up the bag and use it as a quilt with the zipper open.
I have a western WM Versalite for cold weather and a ZPacks “quilt” which is really a hoodless sleeping bag. I really like the flexibility of the ZPacks “quilt”, I have it open in quilt mode most of the time, but if things get a bit drafty and on the cold side, I can zip it up and keep more heat in. I like that both bags (as your WM Ultralight) have continuous baffles so you can “move” the down where you want it (kind off).
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