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Multiferroic oxides have recently emerged as key materials with the potential to tackle the exploding demand for systems that enable efficient energy usage and enhance the functionality of spintronic devices. In this talk, I will discuss the recent development of single-site manganese-based multiferroic perovskite materials, Sr_1-xBa_xMn_1-yTi_yO₃, with ferroelectric transition temperatures boosted to ~430 K. Using a series of temperature-dependent scattering experiments at various pressures, we demonstrate the tunable character of coupling between the magnetic and ferroelectric order parameters and show that ferroelectricity could be easily manipulated through the application of either external or chemical pressures. Measurements of the magnetic and structural properties under pressure allowed the construction of a detailed P-T phase diagram in which the diverse phases are delineated. Impressive spontaneous polarization values of ~30 μC/cm², in agreement with Ti-free Sr_1-xBa_xMnO₃, are calculated using an empirical c/a-based equation or derived from a point charge model with bond-lengths and angles determined by neutron diffraction.