I've carried that exact bag (WM Ultralite) on a lot of trips and have slept a lot of nights in it, perhaps 200 nights overall, and it's a wonderful bag. I've just recently sent mine back to WM to get refilled, and overstuffed in fact a bit. Not that it isn't durable; I think that's a reasonable thing to have to do to any down bag after 4000 miles or so of use.

I've used it down into the teens with puffy clothes inside to beef up the overall temp rating. I've slept with it many a night fully unzipped in sort of "comforter" mode.

I'm not saying that it's the only good choice (!), but it certainly is a fine choice.

The one thing that I suggest w.r.t. down bags is to consider getting one of those "ultralight" dry bags, and size it up. I.e., get a light dry bag that's a bit bigger than needed for your sleeping bag (just look at the stated volume in cc or liters for the provided stuff sack and increase that some). Doing this allows me to compact the bag a bit less when my backpack isn't filled to the brim, yet with the dry bag approach I can just roll it further down to decrease the volume at need.