Hybrid structural systems offer a strategic opportunity to enhance building sustainability by combining materials in ways that capitalize on their primary mechanical properties. By varying floor system configurations, it becomes possible to improve not only structural performance but also the environmental, economic, and social dimensions of sustainability that are inherently interconnected in the design of resilient, resource-efficient buildings. This work presents a comparative analysis of the environmental impact and cost of multi-storey steel buildings featuring three alternative floor systems: (i) discontinuous CLT panels; (ii) continuous CLT panels; and (iii) steel decking with concrete topping. Starting from a preliminary structural design of floor systems based on span length and performance criteria, the study proceeds with the modelling and analysis of full structural frames under varying seismic demands, in compliance with European design standards. For each configuration, material quantities, embodied carbon emissions, and estimated construction costs are assessed through a combination of structural modelling and life cycle analysis tools, including SimaPro. The objective is to identify how different floor technologies influence the overall sustainability of lightweight multi-storey buildings, offering a data-driven basis for more informed design choices