A 3-week-old exclusively breastfed infant presents with poor weight gain (regained only to birth weight by day 21), frequent feeds (10–12 per day), and visible milk transfer during feeds. The mother reports breast engorgement, occasional leaking, and adequate milk supply. On examination, the infant is alert, has moist mucous membranes, and passes 6–8 wet diapers daily. What is the most appropriate next step in management?