i've been using a 48-50" wide hammock for quite a while & like it. that width might help w/ trying the sleeping bag/pea pod.
Mine are this size also. If you making a DIY hammock for your sleeping bag make the sides with a little more slack than normal. If the sides of the hammock are too high it creates an air space between your chest and bag that is harder for your body to heat. I kept re-working mine until it gave me the best fit for my bag. I usually do not promote this setup even though I use it because it will not work with just any hammock and bag. TEST, TEST, and TEST some more before going into any cold weather. When you test in your backyard make sure you stay in for the night not just an hour or so.