A 78-year-old man with benign prostatic hyperplasia (BPH) is taking Tamsulosin 400mcg OD. He presents with ongoing bothersome lower urinary tract symptoms (LUTS), including poor stream and nocturia (x3). His prostate is moderately enlarged on DRE, and PSA is 1.5 ng/mL. Post-void residual volume is 80mL. According to NICE guidelines, what is the most appropriate next step in pharmacological management?