This study delves into the behavior of fly ash-based geopolymer aerated mortar, emphasizing the role of various stabilizing agents in evaluating its potential as a sustainable and lightweight construction material. Fly ash, a byproduct rich in aluminosilicates, is the primary ingredient. The aeration process, aided by hydrogen peroxide (H2O2), improves thermal insulation according to the previous research. To enhance stability and performance, stabilizing agents such as polyvinyl alcohol (PVA), vegetable oil, and sodium lauryl sulfate (SLS) have been strategically integrated. The research rigorously assessed critical physical, mechanical, and thermal properties. At a water-to-binder ratio of 0.4, incorporating a 2% concentration of H2O2 as a controlled foaming agent. Furthermore, using a stabilizing agent minimizes pore sizes and enhances the uniformity of pore distribution, affecting the material's internal structure and bonding mechanisms. The use of PVA results in the formation of isolated pores, whereas the application of vegetable oil and SLS facilitates the creation of connected pore structures. The thermal conductivity measured in this study ranged from 0.07 to 0.15 W/m·K. The results demonstrate that the formation of pore structures significantly influences insulation performance in high porosity, correlating to a decrease in thermal conductivity. This research underscores the substantial potential of fly ash-based geopolymer aerated mortar in lightweight construction, providing key insights into the interactions between stabilizing agents and the material’s properties.