chiro-flow. water-filled pillow.
http://www.chiroflow.com/en/index.html
I've had mine for about six years or so. I LOVE it. I take it with me everywhere. Got it from my old chiropractor - my new one sells them, too. My neck is a mess and tends to get jacked up occasionally, and I'm convinced a bad pillow can trigger that. I still have flare-ups now and then, but I do think this pillow helps.
But also...the chiro would say stomach sleeping is a big no-no for your spine anyway
oops - I missed your statement in the OP about being unable to have water-filled pillows. why is that, though?