HYOH, but I made my own. 3"x7"x2" Synthetic insulation for loft.
When it seems like the night will last forever
And there's nothing left to do but count the years
When the strings of my heart start to sever
And stones fall from my eyes instead of tears
I will walk alone by the black muddy river
And dream me a dream of my own
One more "it works for me but probably won't mean a dang thing to you" comment: I usually only use the pillow to keep my head from flopping to the side, or when I'm on my side. On my back, I don't use it underneath my head....
I use a pillow like the above but it's synthetic. I cinch it up to compress for packing
Like bubba, I like something cradling my neck. For backyard use I use an old Thermarest synthetic pillow It's rectangular Probably 7" x 12"
At home I use a specially-shaped pillow between my thighs to keep my spine straight. Like to have something for side sleeping in a hammock but I can sleep on my back most of the time
I, also, use the JRB Graham Air. However, I don't use it under my head--I find the hammock provides enough support for my head and neck. Instead, I use it under my (usually left) knee, to prevent knee hyper-extension in my Hennessy.
Otherwise, I would need to maintain a figure-4 position all night, and that gets kinda old after a while.
I have a Wilderness logics synthetic. Never really thought I needed a pillow. Their design is light and narrow, mostly for neck support. My shoulders and head stay on the hammock and I stuff the pillow in the space under my neck for support. Works better than I'd hoped. No more crick in the neck come mornin.
Pretty much as you've determined a pillow and it's use is an individual choice. Back in my bed days I slept with 2 pillows. Now that I'm a fulltimer, on my back I don't need any, and on my side I use a WM travel pillow only 1/2 inflated. Keep looking you will find your own ideal pillow.
Most of us end up poorer here but richer for being here. Olddog, Fulltime hammocker, 365 nights a year.
I find that I need a very minimal pillow. One thing you may want to try is tieing it with some chord to the gathered end, so it hangs about where you want it. This way you will not be chasing it all night. and it will not flop out on the ground when you get in and out. Mine just stays in the hammock full time.