A 75-year-old man with known benign prostatic hyperplasia (BPH), treated with tamsulosin, presents with increasing urinary frequency, urgency, and nocturia over the past 3 months. His PSA level is 2.5 ng/mL (stable from previous). Digital rectal examination reveals a moderately enlarged, smooth prostate. Post-void residual volume is 80 mL. According to NICE guidelines, what is the most appropriate next step in management?