A 68-year-old male with COPD (GOLD Stage 3, FEV₁ 38% predicted) on ICS/LABA therapy presents to the emergency department with acute dyspnea, increased sputum purulence, and fever (38.2°C) for 2 days. Chest X-ray shows no focal consolidation. Arterial blood gas: pH 7.32, PaCO₂ 58 mmHg, HCO₃⁻ 28 mEq/L, PaO₂ 62 mmHg on room air. Which of the following is the most appropriate initial management?