For a healthy 20-day-old baby, a standard, whey-dominant cow's milk-based infant formula (often labelled Stage 1) is highly recommended. These formulas are specifically designed to mimic breast milk and are easy for your newborn's delicate digestive system to digest. Unless your paediatrician advises otherwise due to allergies or sensitivities, there is no need for specialised formulas like soy or lactose-free. Please consult your paediatrician before making a final selection so they can confirm it aligns with your baby's weight and growth needs. You are doing a wonderful job caring for your baby!