You've stacked pillows before. Felt a second of "oh wait, this is better," then watched them collapse 30 seconds in. Mood gone.
Bed pillows are 20-30 kg/m³ foam. They squish. The EROA Spark Pillow is medical-grade 60 kg/m³ memory foam, locked at a 27° angle, non-slip base. She moves, it stays. You go harder, it stays. Two hours in, it's still at 27°.
You were right about elevation. You just needed the version that doesn't quit on you.