Temperature is a crucial factor influencing the quality of sleep, as it directly affects thermal comfort during sleep. The present work reports the investigation of the thermal performance of high-density (HDF) and low-density (LDF) polyurethane foam mattresses impregnated with sodium-based Phase Change Materials (PCMs) and their efficacy in temperature buffering features. A controlled laboratory study comparing exposure to these mattresses was conducted by installing mattresses in an insulated wooden box and simulating body heat with incandescent light bulbs. Ten different mattress designs were tested, including variations such as the addition of PCM and perforations for maximum heat dissipation. A multichannel record system and a hygrometer were employed to constantly monitor the temperature and relative humidity, respectively. The results were both statistically significant and reliable, as confirmed by error and ANOVA tests (P < 0.0001). Among all the samples, it was found that PCM1/LDF possessed the most efficient thermal regulation capacity at a temperature difference of 6.98 °C, which is most suitable for improving sleep comfort. These results provide a way to enhance user thermal comfort by providing informative data for better mattress design.