you'll definitely need one marked -long or -tall. Mummy bags are warmer and lighter but they are a little more restrictive if you move around a lot. You'll be tired though so it won't matter. Mummy bags are definitely better. If the toebox is tight, you'll compress the insulation and your feet will get really cold.

I have a North Face Flight that I like a lot. Its rated at 40 or 45 degrees but I've had it out down to around 20 and been comfortable enough. I just use a Z-Rest pad because its only a pound and you can't pop it. Its definitely not luxurious but its warm and comfortable enough.

If you won't be inside a tent, you'll definitely need a warmer bag. A bag liner is really nice. Its like a sock. It keeps your bag from getting all funky and you can easily wash the liner. It also makes the bag a little warmer. I have a silk one.

Bags with a pouch in the hood give you a place to put something soft that won't move around. you can get an air pillow or just shove a jacket it in. I'd also look for insulation at the zippers (like a big puffy straw) and its really nice if they have something at the collar bone. If not you can always use a scarf to plug the air leak.

I've never used a vapor barrier because I really don't like being damp, but they supposedly hold a lot more heat it and don't weigh very much.

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