I just have a random thought to throw out there. Has anybody ever used one of those airplane neck pillows for a hammock pillow? I’m really happy with my homemade pillow but now I’m thinking I tried to reinvent something that’s already easily available.
Just a thought as I anticipate a Tuesday launch into Quetico.

I have an inflatable foam pillow from MEC. I only use it about 10% of the time in my hammock. And when I do, I don't inflate it. It's obviously a personal thing. I use a fairly flat pillow in bed and cringe when I'm at a hotel and their pillows are the size of hot-air balloons.

The gentle slope of the hammock suits me well. I have tried the pillow you describe and never liked it

I’ve found that stuffing my light weight puffy coat into my sleeping bag stuff sack makes a comfy pillow. To your point though, I find it most comfortable when I put my pillow under my neck rather than my head. Maybe you’re on to something with the airline pillow. I did try an inflatable version of one but didn’t find it to be very comfortable. Maybe a plush, non-inflatable version would be more comfortable.
I tend towards the single portage/ultralight spectrum so I’ll probably stick with my stuff sack/puffy coat combo.
Let us know what you figure out.

I don't fly very often so if the u-shaped neck pillows often seen at the multifunction stores along highways (gas stations) is what you mean I love them and have used them when I truck camp. Paddling or hiking in I am just fine with something rolled up in a soft bag. I also prefer the neck pillow and cringe at hotel pillows.

I tried the neck pillow on my red eye flight to Duluth. It’s one of the inflatable ones so I figured I’d adjust it for comfort. Maybe I just don’t sleep on planes very well anymore but it only marginally helped. I just went with my custom V shaped pillow and it worked great. It also has tether cords so it stays in place. Especially when I achieve “the Perfect Hang”
Airline neck pillow study abandoned

Like Tundra, I stuff my puffy coat into a thin pillow case that is smooth or cool on one side, and has soft insulation on the other. Depending on the weather I flip it over. The pillow case is about 12 x 15.I have a ridgerunner and too tall a pillow kinks my neck, a puffy coat can be made to any thickness once contained in a pillow case. Mostly it's just under my neck for support.I've tried about every style pillow, this for me is perfect with no extra gear, I trip mostly in the spring and fall so always have my down coat.