This study focuses on enhancing the performance of a single-axis Microelectromechanical Systems (MEMS) accelerometer operating in in-plane mode and employing capacitive sensing and static mode operation. The investigation introduces a compliant mechanism-based displacement amplifier to optimize the Advanced Mechanical Preamplifier for the Accelerometer Combined with Capacitive Measurement System (AMPACC) MEMS accelerometer design. The lever-based displacement amplifier is analyzed for modal and electromechanical characteristics, with optimization targeting the desired natural frequency and maximum sensitivity in comparison to existing designs. In this work, an AMPACC MEMS accelerometer is designed with free-form geometries (FD) rather than orthogonal design (OD) to provide greater flexibility in dimension adjustments for optimization. The lever beam is further optimized, allowing curvature for increased mechanical sensitivity compared to conventional designs. An analytical model for AMPACC with an orthogonal design is developed, demonstrating good agreement with existing literature in terms of natural frequency. MEMS+ numerical simulations demonstrate that the proposed design achieves a first-mode natural frequency of 458.62 Hz and a sensitivity of 1.875 \(\upmu \) m/g. The outcomes highlight the superior performance of the optimized lever beam (OLD) design, showcasing a remarkable 210% enhancement in displacement sensitivity in a closed-loop configuration compared to existing models. Additionally, our investigation extends to exploring the impact of various parameters, including sidewall angle, suspension spring, and proof mass dimensions, on the sensitivity of the MEMS accelerometer.