Shifting the down in the Ultralite only works if you don't turn over! Otherwise, you are better off to make sure the down is distributed evenly in each baffle. I've found I need to check mine every couple of days.

I've taken the Ultralite down to 15*F, wearing my jacket and a fleece balaclava, and--with a well-insulated pad--was very comfortable. That 1/8" foam that was suggested won't be enough with an uninsulated air pad and may not be enough with some insulated air pads.

With the Ultralite, it's also important to tighten up the draft collar really snugly around the neck. With the draft collar tight, I was able to keep the hood loose so I wasn't breathing into the down (something you never want to do!).

It is really important in cold weather to eat a hot meal and have a hot drink in the evening, preferably something with some fat in it which your body will metabolize slowly during the night. It's also important to be hydrated (dehydration contributes a lot to both altitude sickness and hypothermia). You may also have been suffering from a lack of electrolytes on your climb. A high carbohydrate diet also helps with the altitude. Finally, even 5 minutes of vigorous exercise just before crawling into bed will get your metabolism stoked up so you'll have enough body heat to warm up the sleeping bag. I learned all this the hard way!