are you rubbertramping, trekking or leathertramping?
size & weight are a definite issue, as well as when & where you will be..
any bag you take for leathertramping should be geared specifically to *your* personal use.
that is safest & healthiest for both of you.. don't get two 40 degree bags, as warm as 2 bodies are, just because they zip well & are thick & comfy.
if a vehicle is involved, & you want humongo comfort, see if you can find 2 twin size sleeping bags & zip *those* fuckers together...
blankets for 2 are like blankets anywhere.. give & take. & take... &... ; )
so yeah.. the zip-together idea will prolly be sweet..
i tried to double zip, some time ago, but it turned out, with *those* bags, that one of them had to face inside out for the insertion pin to mate with the others retainer box.. -- already sounds fun! : )
there's a lot of good material on StP about equipment.. dunno if your question has ever come up, but maybe..
here's a link to a coleman how-to video:
www.youtube.com/watch?v=jz7nkighauM
size is a major issue, too.. i mean, foot travel requires small, where possible, so there won't be a lot of coziness..
but if yer banging around in a little wagon, with a cargo carrier & your main sleep will be there, then a couple of quilts will do.
if you're going to park & hoof for not more than 3 nights, or not more than a few miles from your base, take the comfy stuff & see how you feel after the first excursion.. you can come close to what you want, first out, with thought, but experience will teach you fast.
good luck & feed people, when you can!!
: )