Promoting sustainable consumer behavior is now an obligation under new European legislation, requiring Life Cycle Assessment (LCA) for accurate environmental impact evaluation. Portugal is a key textile producer, edge in competitiveness in sustainable textile production, driven by electricity-reduced carbon footprint and closed-loop manufacturing. Additionally, while simple spreadsheets can estimate a product's carbon footprint, openLCA software, combined with ecoinvent database, greatly enhances environmental footprint calculations by integrating diverse impact categories, otherwise difficult to estimate. In this study, openLCA is used to evaluate the environmental footprint of a white T-shirt made in Portugal, with 50% recycled cotton from post-industrial wastes combined with 50% organic cotton from Turkey, to assist the design of environmental key performance indicators (KPI). The RECIPE and EF method (adapted) are used to calculate the environmental impacts and allow aggregation in a single score. The KPI related to the global warming impact is validated using a spreadsheet calculator. We propose an “Envi-Score” based on an A to E classification for benchmarking and better communication with the buyers. E is set as the normalized environmental impact of the European benchmark for a mixture material T-shirt encompassing cradle-to-gate boundaries. The introduction of recycled cotton proves to be environmentally beneficial over organic and conventional cotton. Organic cotton proves to be beneficial in comparison with conventional cotton for most environmental categories, except to the ones affected by the lower production yield, for example Land Use. The hotspots for the main impact categories are identified and finally proposed a labelling scheme, to clearly inform about the environmental performance of the products and avoid greenwashing, with the “Envi-Score” rate, carbon footprint, land use and water depletion.