Overcoming current limitations on laser-driven ion energies requires the development of advanced acceleration mechanisms with enhanced efficiency. Here, we present particle-in-cell simulations of a hybrid ion acceleration scheme based on optically tailored plasma density profiles. Ions are initially pre-accelerated in a near-critical density plasma slab via hole-boring Radiation Pressure Acceleration, before being self-injected into an electrostatic field, co-propagating with the driving laser pulse, in a relativistically underdense rear-surface density gradient. This phase matched configuration enables sustained ion acceleration over an extended plasma length. Using Bayesian Optimisation, we tailor the density profile for a fixed laser power, achieving 2GeV maximum proton energies with currently achievable laser parameters. Compared with laser acceleration from ultrathin foils, the maximum proton energy exhibits a markedly steeper scaling with laser intensity, highlighting the potential of target density tailoring for next-generation laser-driven ion sources.