A 50-year-old man with chronic kidney disease stage 4 (eGFR 25 mL/min/1.73m$^2$) secondary to diabetic nephropathy presents with fatigue. Blood tests show Hb 9.5 g/dL, MCV 88 fL, Ferritin 30 ng/mL (low), TSAT 15% (low). Iron studies confirm iron deficiency. What is the most appropriate initial management for his iron deficiency anaemia according to NICE NG233?