<p>Textile-based triboelectric nanogenerators (T-TENGs) have broad prospects in the wearable field due to their excellent breathability, biocompatibility, and low manufacturing cost. The most representative cotton fabric substrates are often limited by their weak frictional polarity and limited output. The current functional modification relies on cumbersome deposition processes and is costly. Therefore, in this study, the self-assembly properties of chitosan (CS) and tannic acid (TA) were utilized to construct a functional coating on the surface of cotton fabric through a simple layer-by-layer immersion method. This simple and low-cost design significantly improves the electrical output while maintaining breathability, resolving the contradiction between comfort and performance. The optimized T-TENG achieved an output voltage and current of 80 V and 0.23 μA, respectively, under 3 N and 5 Hz conditions, which are about 3.5 times higher than that of the unmodified device. The maximum power density can reach 36 mW/m², and after 12,000 mechanical cycles and long-term washing, its output remains stable. This device can not only drive an electronic thermo-hygrometer, light up 160 LED lights, but also serve as a highly sensitive self-powered sensor to accurately capture multi-joint movements and gait characteristics. More importantly, the pressure ulcer warning system developed based on the 2 × 2 sensor array of the modified devices has successfully achieved real-time monitoring of long-term bedridden patients and issued alerts for prolonged immobility. This work provides a new solution for developing intelligent medical wearable fabrics that are both comfortable and clinically valuable.</p>