One though that comes to mind is sewing to rectangles that when sewn together will give you the width hammock you want.
When sewing the two sides together, leave an unsewn section for your arm. but you would probably need to curve that section so it will not squeeze your arm.

I deal with sleep apnea too, and it has worsened in recent years.
The last group hang I went to recently, Yates Place in The Uwharries, NC, it woke me about 3am and was never able to go back to sleep.
Another thing to consider is using an insulated, inflatable pad. I use one and it helps with aches and pains.

I am working on another idea, since the sleep apnea has increased at home and camping/ backpacking. And I can't afford the mini CPAP and battery that I could take backpacking.

I'll share it when I see how well it works.