A new binning method is introduced to select a standard set of quasars (QSOs) for use as cosmological standard candles. This method avoids circularity by using a flux-flux relation and accounts for selection biases and redshift evolution. The procedure allows for the identification of a 'gold' sample of QSOs with reduced intrinsic dispersion in the UV-X-ray flux relation, from which the matter density parameter Ω_M is determined as 0.240 ± 0.064. This value aligns with results from the ΛCDM model using type Ia supernovae (SNe Ia). The methodology involves a robust regression approach, specifically the Theil-Sen estimator, to minimize the impact of outliers and ensure the reliability of the results. The 'gold' sample is defined by a combination of stringent selection criteria and a σ-clipping procedure, resulting in a sample of 1253 QSOs up to z = 7.54 with a reduced intrinsic dispersion of 0.096 ± 0.003. The analysis shows that the results are independent of the initial value of the Hubble constant H₀ and that the matter density parameter Ω_M exhibits only a mild evolution. The study also demonstrates that the 'gold' sample is consistent with other cosmological probes, such as the SNe Pantheon+ sample, within a small deviation. The methodology provides a reliable framework for identifying a high-quality QSO sample for cosmological studies.A new binning method is introduced to select a standard set of quasars (QSOs) for use as cosmological standard candles. This method avoids circularity by using a flux-flux relation and accounts for selection biases and redshift evolution. The procedure allows for the identification of a 'gold' sample of QSOs with reduced intrinsic dispersion in the UV-X-ray flux relation, from which the matter density parameter Ω_M is determined as 0.240 ± 0.064. This value aligns with results from the ΛCDM model using type Ia supernovae (SNe Ia). The methodology involves a robust regression approach, specifically the Theil-Sen estimator, to minimize the impact of outliers and ensure the reliability of the results. The 'gold' sample is defined by a combination of stringent selection criteria and a σ-clipping procedure, resulting in a sample of 1253 QSOs up to z = 7.54 with a reduced intrinsic dispersion of 0.096 ± 0.003. The analysis shows that the results are independent of the initial value of the Hubble constant H₀ and that the matter density parameter Ω_M exhibits only a mild evolution. The study also demonstrates that the 'gold' sample is consistent with other cosmological probes, such as the SNe Pantheon+ sample, within a small deviation. The methodology provides a reliable framework for identifying a high-quality QSO sample for cosmological studies.