Efficient spin-orbit torque (SOT)-driven magnetization switching in thermally robust heterostructures with large perpendicular magnetic anisotropy (PMA) is crucial for next-generation magnetic random access memory (MRAM). β-W is a promising candidate due to its large spin Hall angle and high compatibility with CoFeB/MgO-based magnetic tunnel junctions. However, it tends to undergo a phase transition to α-W upon high-temperature annealing, which can significantly reduce the spin Hall angle. Here, we report that amorphous WTaB/CoFeB/MgO heterostructures grown by magnetron sputtering and annealed at temperatures up to 450 ℃ exhibit strong PMA, high thermal stability, and efficient SOT manipulation of magnetization states, primarily due to the addition of boron (B). Structural characterizations via X-ray diffraction and cross-sectional high-resolution transmission electron microscopy demonstrate the amorphous nature of the WTaB buffer layer and (001)-oriented CoFeB/MgO stack after annealing. Magnetization measurements by vibrating sample magnetometry reveal an effective PMA field as high as 350 mT, even after annealing at 450 ℃. Furthermore, current-induced magnetization switching was achieved with a critical switching current density J_c as low as 2.4×10¹⁰ A·m^–2 under an assistant field of 200 mT, indicating a lower current-switching threshold for the WTaB layer compared to previously reported in β-Ta and β-W systems. The damping-like torque and field-like torque effective fields (H_DL and H_FL), as well as the spin Hall angle of amorphous WTaB, were determined through harmonic Hall voltage measurements. For the initial magnetization-up state, H_DL and H_FL per unit current density were –8.2 mT/(10¹¹ A·m^–2) and –1.8 mT/(10¹¹ A·m^–2), respectively; for the magnetization-down state, they were 7.6 mT/(10¹¹ A·m^–2) and –1.4 mT/(10¹¹ A·m^–2). The magnitude of H_FL is much smaller than that of H_DL, suggesting a weak contribution from the interfacial Rashba effect to the total SOT, with the bulk spin Hall effect in the WTaB buffer being the dominant source. The spin Hall angle of WTaB was approximately –0.44, in agreement with the reported values in in-plane magnetized systems measured by spin transfer torque-ferromagnetic resonance. Our work demonstrates that amorphous WTaB is an efficient charge-to-spin conversion material, holding great potential for the development of low-power spintronic devices with perpendicular magnetization.