With an ongoing upper back/neck problem for the last 30 years I second and third using a pillow between your knees (side sleeping) or under your knees (back sleeping) for resolving pain from sleeping.
In addition to trying a bridge hammock for a flatter lay, try adding an inflated pad (use a double layer hammock). You can adjust the amount of inflation so that you get as hard a surface as you want.
Patience and trial and error will get you into a hammock set up that will give you the sleep that you deserve.
Oh, and you can always use a large enough tarp set-up that the two of you can 'sleep in one tent'.