Single-photon detection in the microwave domain has recently emerged as a powerful tool for quantum sensing, offering a path beyond the standard quantum limit of linear amplification since their sensitivity is set by their dark-count rate rather than by the vacuum fluctuations of the detected field. Superconducting qubit-based single microwave photon detectors (SMPDs) encode the absorption of itinerant photons into discrete quantum states via engineered, non-destructive interactions. A previously demonstrated implementation based on four-wave mixing achieved high efficiency, but remained limited by residual qubit excitation and thermal noise at the detector input. Here, we propose and demonstrate a new SMPD that relies on two cascaded four-wave mixing processes. The information on photon detection is encoded on two spatially separated qubits, which mitigates noise due to uncorrelated qubit errors. Furthermore, increasing the detection frequency up to 11.7 GHz reduces input thermal noise. These combined advances lead to a record-low power sensitivity of 2.4 · 10⁻²³W/√Hz over a bandwidth of 230 kHz.