This study presents the fabrication and optimization of a high-performance polysulfone/polyethylene glycol (PSf/PEG) forward osmosis (FO) membrane incorporating a poly(vinyl alcohol)/glutaraldehyde (PVA/GLA) cross-linked interlayer to enhance water permeability while suppressing reverse salt diffusion. A novel draw solution comprising 1.0 M trisodium citrate and 0.5 mM Triton X100 was employed to evaluate membrane performance. Response Surface Methodology (RSM) using Design-Expert 13 was applied to optimize PEG content, GLA dosage, and casting-knife thickness, with water flux (Jw) and reverse salt flux (Js) as response variables. The optimized membrane, fabricated with 10.12 wt% PEG, 1.14 mL GLA, and a casting thickness of 150 µm, achieved a high Jw of 21.48 LMH and an ultralow Js of 0.13 GMH using deionized water as feed, corresponding to an exceptionally low specific salt leakage (Js/Jw) of 0.006 g/L. This enhanced selectivity can be attributed to synergistic interactions between Triton X-100 and trisodium citrate. Specifically, the hydrophobic adsorption of Triton X-100 may partially constrict membrane pore pathways, while trisodium citrate contributes high charge density, strong electrostatic repulsion, and increased osmotic pressure, collectively improving separation performance. The optimized membrane could maintain water fluxes of 15.31 LMH and 5.32 LMH when treating brackish water (5 g/L TDS) and seawater (35 g/L TDS), respectively. These results demonstrate a scalable and effective membrane-draw solution strategy for next-generation FO systems with high water productivity and minimal salt back diffusion.