Computational and experimental data were combined to develop design rules for rare-earth disilicates to enable tuning of thermo-mechanical properties to better match the SiC substrate. In the case of Young’s modulus and thermal expansion, these trends also hold for multi-component systems; while the thermal conductivity of multi-component systems is noticeably lower, indicating the potential of such materials to also act as thermal barriers. These design rules will enable the development of new thermal and environmental barrier coatings with stiffness and thermal expansion engineered to match that of the substrate, while simultaneously having reduced thermal conductivity.