Original Zenbivy Bed

you could get a 40 degree zenbivy quilt synthetic, although it may not keep you warm at 40 degrees.. their 25 degree down quilts are at $230 if you're willing to cough up a little extra, but they may be too warm. i started sweating in 50 degree weather.

35 degree down alps mountaineering quilt. 1.5 pounds. Maybe the best piece of equipment that company has ever made. Or a zenbivy 25 down same weight. Depends on how windy, how much other clothes a I want to wear. Get off the ground if you can with a cot- car camping. Way warmer as the ground is 10x denser than air and sucks the warmth into the ground. A cot also offers better ventilation and you will have to practice venting vs cold.  At some point it will be too cold for you in a 3 season tent and go with a warmer sleep system-   insulated mat with a good r value, wool liner, light wool gloves and balaclava, 0 bag, new tent. Hot water bottle wrapped in your thickest sock stuffed in your bag! Like the folks say here- new dry clothes on a dry body in a dry tent. I've slept in cold on purpose and some really horrible mistakes have been made. 41 is entering the cold zone. 

If you’re claustrophobic, a quilt is definitely the move. I switched to a Zenbivy bed and it changed everything, it feels more like a real bed, and my dog loves curling up on the corner of it.

I would go with a quilt, they are great for moving around. Zenbivy is most peoples favorite, I really enjoy my Big Agnes.

Zenbivy makes nice options for a couples mat and sleeping bag. I haven’t tried the couple one but I love my hiking quilt and sheet that I have from them. Their system stays clipped in so that when you turn over your quilt stays put and does not get draughts. Best sleep I’ve had when hiking

Any thermarest bag is a good start and I've just tried out the ZenBivy and so far absolutely love it. Would also say that a good sleeping mat goes a long way to keep you warm. You could have the best bag for the cold but a weak mat can undo all the work of a good bag!

Seconding this. I've had mine for years and have never felt confined or cold.