Although ample evidence has demonstrated that daytime napping is beneficial for health and cognitive performance, bedding for napping has not yet been scientifically investigated. In this study, we assessed the effect of a bean bag chair (BC), which would automatically adjust according to body shape and size, on daytime napping and physiological parameters related to sleep, such as electroencephalogram (EEG), electromyogram (EMG), and heart rate variability (HRV). Fourteen healthy participants were enrolled within the context of a randomized, single-blind, crossover study to evaluate the effects of a BC in comparison with those of a urethane chair manufactured to have a similar shape (UR). EEG analyses revealed no significant differences in sleep architecture or frequency components; however, a significant decrease was found in EMG recordings in the trapezius muscle, which represents the neck region (p = 0.024). Additionally, a significant main effect of bedding in the LF/RF ratio (F [1, 20] = 4.314, p = 0.037) was revealed. These results suggest that napping with a BC may provide a comfortable napping environment involving muscle relaxation and proper regulation of autonomic nervous function.