The healthiest pillow is the one that maintains neck–shoulder alignment in your sleep position, fits your skin/respiratory sensitivities, and retains shape over time. Health is about fit as much as material. For side sleepers, it should fill the shoulder gap; for back sleepers, it should support the neck without elevating the head excessively. If you sweat easily or have allergies, breathable materials, low-odor options, and washable covers matter. The best indicator is functional: less morning neck/shoulder pain and fewer nighttime awakenings. Focus on personal measurements and consistent use rather than a single brand or model.