Check the Big Agnes bag carefully before you buy it. I don't know about this particular bag, but the bags on their website are very clear: they are designed without any bottom insulation, and you insert a sleeping pad (naturally, they recommend one of theirs) in the sleeve that forms the bottom of the bag.

I'm not knocking their bags; this is just something you need to be aware of if you're considering one of them. (I have no experience with their bags, but haven't heard anything that would make me shy away from them.)