Developing nanoengineered, efficient, self-powered, flexible, and lightweight wearable triboelectric nanogenerators (TENGs) for detecting real-time human movements is challenging. We employ a novel metal-coupled NaYF4 dielectric matrix prepared in-situ and doped with lanthanide ions (NaYF4:Yb,Er@Au nanocomposites, NCs) to minimize triboelectric losses and facilitate charge transfer in Ecoflex (EC). Polyester cloth (PC: tribopositive) and EC + 0.5–2.5   wt.% of NC (tribonegative) layers with and without polymer spacers are used to fabricate TENG devices for application in low-power wearable electronics. After incorporating 2% NC into the EC layer, the pristine PC/EC-based TENG demonstrates 7.5-fold (56   V to 420   V), 6-fold (1.4   µA to 8.5   µA), and 3.8-fold (18.2 nC to 70 nC) enhancements in open circuit voltage, short circuit current, and charge accumulation, respectively, under 5   N and 5   Hz. COMSOL simulations support the generation of potential distributions. The device without Au nanoparticles exhibits poor performance (179   V, 5.4   µA). The PC/EC + 2% NC TENG produces a power density of 3.7   W   m-2 and powers a stopwatch and 100 light-emitting diodes. Finally, a spacer-free flexible, wearable triboelectric sensor is fabricated, which detects human activities and yields a stable and reproducible 6   V output. This performance is the highest to date achieved using this material class, demonstrating the potential for developing consumer wearable electronics.