DS didn't camp till he was 4mo, and we did co-sleep on an air mattress and nursed at night.
I'm a single parent, though. We used a queen mattress.
What I do is make a bed like my bed at home. I do this even when I sleep alone. I put a couple towels on the air mattress, then the sleeping bag, open all the way, and inside-up. The towels are to keep the vinyl outside of the bag (or whatever it's made of) from slipping off the mattress.
Then I make the bed, like a normal bed. I put the fitted sheet on, and anchor it around the corners of the air mattress with sheet garters. Then I put on the top sheet and blanket and comforter. And bring extra blanket in case.
For ds-- I finally found out what those long-sleeved onesies were for! He had bare legs, because the bag is warm
-- it's rated for -20, I think-- and he likes to sleep with his arms out. I had a onesie with long sleeves and a turtleneck for camping.
And a hat is essential. The kind that velcros under the neck. Make sure before you leave (try it) that when your baby turns her head, the hat turns with her, you know, so she doesn't turn her head and the hat stays in place, thereby blocking her airways. If that makes sense online!
You can maybe get little mittens, too.