This study investigates the development of sustainable mortars for extrusion-based 3D concrete printing (3DCP), combining Portland cement with limestone filler and recycled glass powder (GP). The goal was to reduce clinker content without compromising printability or structural performance. A Design of Experiments (DoE) strategy using Central Composite Design (CCD) was applied to assess the influence of mix parameters on workability, strength, and environmental indicators. Mortars derived from optimised binders were validated through laboratory and large-scale printing. Results indicate that cement content can be lowered to around 400 kg/m3 while achieving compressive strengths above 55 MPa and reducing Global Warming Potential (GWP) to approximately 390 kg CO2-eq/m3. Printing trials confirmed good extrudability, layer bonding, and dimensional accuracy. These findings highlight the potential of low-clinker mortars for sustainable additive manufacturing in construction.