Monolayer ternary tellurides based on alloying different two-dimensional (2D) transition metal dichalcogenides (TMDs) can result in new 2D materials ranging from semiconductors to metals and superconductors with tunable optical and electrical properties. Semiconducting WTe2xS2(1-x) monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with circularly polarized light (CPL). The degree of valley polarization (DVP) under the excitation of CPL represents the purity of valley polarized photoluminescence (PL), a critical parameter for opto-valleytronic applications. Here, we present new strategies to efficiently tailor the valley-polarized PL from semiconducting monolayer WTe2xS2(1-x) at room temperature (RT) through alloying and back-gating. The DVP at RT is found to increase drastically from < 5% in WS2 to 40% in WTe0.12S1.88 by Te-alloying to enhance the spin-orbit coupling. Further enhancement and control of the DVP from 40% up to 75% is demonstrated by electrostatically doping the monolayer WTe0.12S1.88 via metallic 1T′-WTe2 electrodes, where the use of 1T′-WTe2 substantially lowers the Schottky barrier height (SBH) and weakens the Fermi-level pinning of the electrical contacts. Our demonstration of drastically enhanced DVP and electrical tunability in the valley-polarized emission from 1T′-WTe2/WTe0.12S1.88 heterostructures paves new pathways towards harnessing valley excitons in ultrathin valleytronic devices for RT applications.