When evaluating soft foam pillows, the primary focus should be on foam density and recovery time. For high-quality memory foam, a density of 3lb/ft³ to 5lb/ft³ is ideal for balancing softness with support. Ensure the supplier uses CertiPUR-US® certified foam, which guarantees the product is made without ozone depleters, PBDEs, or heavy metals. Additionally, check the Indentation Load Deflection (ILD) rating; a lower ILD (around 10-15) indicates a 'softer' feel preferred by side and back sleepers.