Thermoelectric sensors, which are capable to convert temperature gradients into electrical signals, hold promise for use in wearable body-temperature monitors and self-powered electronic devices. However, traditional flexible thermoelectric devices constructed with organic materials have been hampered by their low energy conversion efficiency, largely stemming from the lack of ideal materials and optimized device geometry. In this study, we utilize state-of-the-art Ag2S-based inorganic materials and fine-tune the geometric parameters of full-inorganic flexible thermoelectric devices through finite element simulation. Our research reveal that these geometric parameters significantly impact the output performance of the flexible thermoelectric device. With the temperature difference set up as 25 K, the optimized device demonstrates a notable performance enhancement, particularly in terms of power density, which is 84% higher compared to the pre-optimization state. This work introduces a novel approach for enhancing the performance of full-inorganic flexible thermoelectric devices, and also delves into the potential application of this technology in the realm of respiratory monitoring, underscoring its significance and promising prospects.