We prove that the upper electronic bands of k-phase BEDT-TTF salts are adequately modeled by an half-filled tight-binding lattice with one site per cell. The band parameters are derived from recent ab-initio calculations, getting a very simple but extremely accurate one-electron picture. This picture allows us to solve the BCS gap equation adopting a real-space pairing potential. Comparison of the calculated superconducting properties with the experimental data points to isotropic s_0-pairing. Residual many-body or phonon-mediated interactions offer a plausible explanation of the large variety of physical properties observed in k-phase BEDT-TTF salts. ; Comment: 8 pages, 6 PostScript figures, uses RevTeX