If you sew a pouch with built in attachment points, which is very easy to do/sew, using say, 1.1 oz/yd, or .9oz yd from diygearsupply, cheap too, you could just use cord to wrap around the mattress. Very hard to sew an existing pillow, though I guess you can sort of cinch the top/bottom together and sew on a loop of 1/2" material or strapping to use as connectors.
I'm starting to suspect that for UL, where you, as correctly noted in this thread, don't have extra bulky clothing to stuff into a stuff sack, or you can't count on it being unused that night, and, given that air pillows just suck (as far as my sleeping style is concerned anyway, or if you move around at all at night), and that down compresses too far to be an actual side sleeping support unless you make the thing so big it's far heavier and bigger than makes sense, mixing media is the best way to go, with a touch of creativity added in.
I sleep on my side, so it's hard to get that pillow height without a fleece jacket or whatever to use as a pillow. Fleece is certainly the best material I've ever used to make pillows, specifically because it's both soft and essentially non compressible, it's just very bulky and heavy, relatively speaking. But I should now that I think on it re-weigh a fleece jacket and oppose it to an alternate pillow setup plus a light puffy jacket, wonder how close they come.
I was lucky and got a cheap goosefoot down pillow that the guy who runs the company sold one day as seconds on gear swap, but very small, with a built in pocket to stuff something in, I shoved some light, compressible, 1" thick egg crate type foam into it, packing stuff, and realized, oh, I see, you only need the top part to be down, the rest doesn't matter, it just has to raise your head. I can't see trusting zip lock bags, sorry, while interesting, that strikes me as just a 'throw away your gear every few trips and pretend that you are not creating a consistent waste stream into the real environment that we all live in' type of approach to UL, that's an approach I want to remove myself from as much as possible, my gear is already just fine, plenty light enough. As for using inflated platys/evernews, one mistake and ho water holder, that's not smart in my opinion, trip when getting up, whatever, pop, no water container. Now, putting your hiking shoes under your mattress.. .that's something that should work reasonably well if you have some padding over it.