This study evaluates mortars that incorporate mixed recycled aggregates, biomass bottom ash, chamotte, wood waste, and expanded clay as partial substitutes for cement and natural aggregates. Three series of mortars were investigated: with 25% cement replacement, partial sand replacement, and simultaneous replacement of cement and sand. Mechanical, physical, durability, and thermal properties were evaluated, along with their relationships through a correlation analysis. Cement substitution did not result in a drastic reduction in compressive strength and produced limited thermal improvements, whereas sand substitution led to substantially greater reductions in thermal conductivity, ranging from approximately 10.3% for MRA to 59.1% for wood waste compared to the control. Expanded clay reduced thermal conductivity by 24.7%, while BBA-L showed greater insulating potential than BBA-PG but resulted in a reduction in compressive strength. The combination of chamotte, limestone filler as a cement substitute, MRA, and expanded clay as an aggregate substitute provided the best balance between thermal and mechanical performance, achieving a compressive strength of approximately 39 MPa at 90 days and reducing thermal conductivity by nearly 22% compared to the reference mortar. The results demonstrate that thermal performance depends largely on density and porosity, although the optimal selection of materials requires simultaneously considering both mechanical and physical properties.