In this study, non-functionalized carbon nanotubes (CNTs) with high aspect ratios and different lengths were used to prepare two stable, homogeneous formulations for textile applications. CNTs were mixed with an amino-functionalized sol-gel precursor and a thermo-degradable surfactant that facilitated the dispersion and distribution of CNTs by acting on the π-π stacking interactions while preserving their conductive properties. The use of a polyurethane thickener led to CNT-based pastes, which were applied to cotton fabrics using the knife-over-roll method, producing electrically conductive textiles. Different chemical-physical techniques were employed to confirm the efficacy of the procedure and assess the morphology and chemical composition of coatings. Electrical properties were evaluated by surface resistance measurements, demonstrating that shorter CNTs lead to higher conductivity at the percolation threshold. The electrically conductive CNT-based cotton fabrics, integrated with an optoelectronic system, acted as elements of signal transmission of biomedical data by reliably monitoring heart rates through photoplethysmography. This work highlights the successful combination of CNTs, the sol-gel process, and cotton fabrics, resulting in efficient and unobtrusive smart textiles suitable for various applications, including healthcare and sports.