The lady-friend and I use a 2-person, 2 lb, 32F quilt. We may up it to a 20F that's also slightly larger (she's prone to rolling over in the night, leaving me rather literally freezing, so the extra surface area will be a big difference to me).

To keep the pads together we sewed foot and head sleeves that wrap around the pads. They do the job well and weigh 1 oz. Maybe. If even that. They're totally worth it rather than a gap forming between the pads and someone ends up partially on the cold ground.

We both use sleeping bag liners on nights it's colder than comfortable to use just the quilt.

There is always the option to zip two bags together, but zippers are heavy and we never feel the need the to be separate. Either it's cold and we greatly enjoy the shared body heat or it's so warm we don't need to sleep under anything, but those days are so seldom and few anyhow. Yes, after a few days we both smell terrible, but sleeping together doesn't change that. You just get used to the way your partner smells in the same way you get used to your own smell. Like many minor inconveniences when thru-hiking, the smell of your partner is something that you will be a whole lot better off if you just learn to deal with it.

When we met and started hiking together to the AT, we tried the zipping together bag thing. It's not as ideal for several reasons: 1) Weight; 2) Awkward positioning; 3) Zippers are thin points in the insulation and, therefore, inherently cold; 4) More difficult to pack up inside the tent on rainy days.

In all my hiking I've only encountered one hostel that didn't allow couples to sleep together. It was in Damascus, VA. I think it was called The Place. The lady-friend and I weren't together then, so it didn't really matter, but that kind of scenario is the only trouble I see with using a 2-man quilt.

In summary, I recommend a 2-man quilt for couples so long as you are both sure you will two will always end up together at the end of the day. Among the aforementioned benefits, I found my leg muscles were so much more relaxed in the morning from the other's body heat to keep them warm in the night. It made a massive difference in how my legs fared thereafter.