Warm mittens are necessary for Lhotse. Please don't frostbite your hands. We prefer mittens to gloves, as mittens are so much warmer. We are not sure who makes the best gloves. The warmest mittens come with a sturdy Goretex outer shell and a very warm polar fleece removable mitten liner.
You won't need to wear any liner gloves inside these mitts (they already have their own integral liner) so fit is very important. In Kathmandu you can find good quality Black Diamond and Mountain Hardwear mittens.