It is a trap to buy a physiological pillow with a fixed curvature, promoted as a universal pillow, not only because few people sleep on their backs most nights but also because 20% of the population in Australia does not have a physiological curvature from birth, but a spine in a straight line. An above-average-weight person will need a higher and more giant pillow, while a short, thin person would work better with a smaller pillow. Analyse the spine-shoulder distance, and choose a higher pillow if you have broad shoulders.