This study numerically investigates the performance of a vapour jet ejector in a heat-driven ejector refrigeration cycle when replacing R134a with R1234yf, a hydrofluoroolefin refrigerant with lower global warming potential, in compliance with F-Gas Regulation restrictions. Numerical analyses focus on improving the primary nozzle exit position, mixing section convergence channel angle, and secondary fluid operating conditions to reduce performance losses for the case of R1234yf instead of R134a. The computational fluid dynamics (CFD) approach was employed using ANSYS Fluent v19.2 for the ejector modelling. Results indicate that substituting R134a with R1234yf reduces the entrainment ratio by approximately 4.1% under similar operating conditions. However, with a +10 °C superheat applied to the secondary fluid and improved values for the primary nozzle exit position and the converging duct angle of the mixing section, the entrainment ratio increased by 10.4% and 13.7%, respectively.