A vapour barrier liner sorts out the problem. You may on occasions be a little moist in the morning but you will be warm and you won't have all that weight and bulk. The thing about carrying a heavy bulky sleeping bag is that you have to use a bigger and, therefore, heavier rucksack, too. You can also have the down in your bag proofed which adds a tiny amount of weight. Everything depends on your priorities and budget. If you want to be comfortable, both in terms of warmth and the weight you carry, down, one way or another, is your best option.