In urban development processes, deep excavations are frequently carried out for the construction of multi-level basements, railway tunnels, and transportation infrastructure. These excavations create significant challenges for engineers due to the need to protect adjacent structures and urban utilities. Therefore, safe excavation requires the application of appropriate monitoring methods and specialized instrumentation. In this study, based on the results of numerical simulations of a soil nail–stabilized excavation using the finite element method, the effects of excavation depth and width, the presence of problematic soil layers, groundwater conditions, and the existence of displacement-sensitive structures adjacent to the excavation on the design of monitoring systems investigated. The results indicate that for deep excavations, the installation of a monitoring system is essential. For measuring vertical displacements, the use of extensometers behind the wall or at intermediate columns is recommended, while horizontal displacements should be monitored using inclinometers installed behind the wall or near intermediate columns. In the presence of groundwater, piezometers should be installed behind the excavation wall. Furthermore, when problematic soil layers are present, load cells should be installed on soil nails at the layer boundaries, and strain gauges and inclinometers should be used behind the wall. The dimensions of the excavation do not significantly affect the monitoring results and do not require additional instrumentation.