The Belle II experiment is evaluating an upgrade program aiming at the time frame 2026–2027 for the installation of the upgraded detectors, to improve the detector performance and robustness against beam-induced backgrounds. The VTX concept, a fully-pixelated system based on depleted monolithic active pixel sensors, has been developed as a replacement of the current pixel-and-strip vertex detector. A simulation framework for the VTX has been developed and integrated with the standard Belle II simulation, facilitating the comparison among different layouts. Simulation results (such as tracking efficiency and vertex resolution) on benchmark physics channels are presented, showing a significant improvement with respect to the current detector.