Ginzburg-Landau-Devonshire models are used to explore ferroelectric phases and pyroelectric coefficients of symmetric free-standing, thin-film trilayer heterostructures composed of a ferroelectric and two identical non-ferroelectric layers. Using BaTiO3 as a model ferroelectric, we explore the influence of temperature, in-plane misfit strain, and the non-ferroelectric layer (including effects of elastic compliance and volume fraction) on the phase evolution in the ferroelectric. The resulting phase diagram reveals six stable phases, two of which are not observed for thin films on semi-infinite cubic substrates. From there, we focus on heterostructures with non-ferroelectric layers of commonly available scandate materials which are widely used as substrates for epitaxial growth. Again, six phases with volatile phase boundaries are found in the phase diagram for the NdScO3/BaTiO3/NdScO3 trilayerheterostructures. The evolution of polarization and pyroelectric coefficients in the free-standing NdScO3 trilayer heterostructures is discussed with particular attention to the role that heterostructure design plays in influencing the phase evolution and temperature-dependence with a goal of creating enhanced pyroelectric response and advantages over traditional thin-film heterostructures.