Mountain Hardwear - Phantom™ 15F/-9C

My current down mummy one from Mountain Hardwear that I got for a crazy deal (<$90). There are zippers on both sides and the toe area. I move a lot in my sleep, and the slightly wider area up top makes it easier. (It's wide enough for my arms to go to my shoulder area, even zipped up.) It's a huge step up from my previous one, a cheap synthetic mummy.

Mountain Hardware has a couple bags that are compatible, my wife and I use them. They are a little bulkier, but affordable. You could also look at something like the Zenbivy Double bed.

I have the Mountain Hardwear and love it. My kid has a North Face Inferno and loves it… and I worry less about water damage. I trust OutdoorGearLab.com for reviews. 

It's really a personal choice. I would suggest you try the MH sleeping bag. It's a free way to test a type of sleeping bag. Worst case, you buy another one later. I personally use down sleeping bags because they are lighter and compress better. But they are more expensive and take a lot longer to dry if it gets wet.