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The residential remodeling market in South Korea is experiencing a compound annual growth rate of 5.4%, yet antiquated multi-family dwellings often feature slender concrete slabs (120–180 ㎜) that restrict the thickness and loading of retrofit systems. This study develops a wet-type floating floor system by jointly optimizing impact sound insulation and the long-term dimensional stability of resilient layers. Structural stability was evaluated via residual deformation (KS F 2873) and time-dependent deflection monitored using an 18 kg steel load plate (approximately 1.96 kPa), where displacement stabilized within 144 hours with deflection below 0.2 ㎜. To suppress low-frequency resonance-induced amplification around 50 Hz, a design target for dynamic stiffness (KS F 2868) not exceeding 5 MN/㎥ was adopted while maintaining residual deformation within 3 ㎜. The proposed multi-layered system—consisting of embossed ethylene vinyl acetate (22–25 ㎜), a sound-absorbing interlayer (12–15 ㎜), and a 3 ㎜ polypropylene board for load distribution—was validated through field tests on a 150 ㎜ thin slab. The optimized configuration achieved standardized impact sound levels of 38 dB for light impact and 47 dB for heavy impact, successfully meeting the performance targets of Grade 2 and Grade 4, respectively. These results validate that the developed system provides superior acoustic comfort and structural durability, offering a robust engineering solution for environmental noise mitigation in renovated dwellings. Future investigations will explore point-support mechanisms and long-term creep tests exceeding one year to further enhance low-frequency damping performance.