Urban Heat Island (UHI) and exacerbated heatwaves impact heat-related mortality and morbidity, deteriorating citizens’ wellbeing and limiting outdoor activities in the built environment. As the built environment has a huge potential in mitigating UHI, diffused green, blue and grey solutions in dense urban areas could benefit resilience. Although the cooling effect of large size parks has been studied, the microclimatic effect of small open urban spaces between the buildings has been overlooked. The goal of this study is to establish a database of solutions identifying the morphology potential of urban voids/pocket parks maximizing thermal comfort towards heat stress mitigation. The research is conducted by means of parametric computational simulations with Grasshopper and Ladybug plugins for Rhino3D. The simulations evaluate geometric configuration, including aspect ratio and orientation to assess thermal performance in the hottest day in Rome, as a significant case study. The study examines Universal Thermal Climate Index (UTCI) values three times of day to capture the diurnal variation in thermal comfort. The analysis reveals that for all aspect ratios, the 315° orientation offers the best thermal comfort in the morning, while the 225° orientation provides the highest comfort during the afternoon. In the evening there is minimal variation in average UTCI across all scenarios. Additionally, as the aspect ratios increase, more pronounced differences in UTCI are observed among different orientations. The findings indicate the potential of small urban voids to act as diffuse resilience (pocket parks), depending on their configuration, as the bases to further improve their performance acting on their components.