Questionnaire
We collected patient information on individual attributes, including age, sex, and body mass index (BMI). In addition, subjective sleep comfort and bed surface firmness were confirmed using a visual analog scale (VAS). Two types of VAS ranges were set as 0 (most comfortable)–10 (worst possible uncomfortable) and 0 (most possible softness)–10 (worst possible firmness). Subjects spent approximately 20 s on the bed and evaluated the perceived firmness and comfort of the bed during this time.