Sling carrier

It really depends on you. For a 3 weeks baby, you can use a woven wrap, stretchy wrap and ringslings because these will fit both you and baby accordingly. If long wraps and rings are not your thing, then a buckle carrier like manduca, emei baby, kokadi flip, etc will be your next best option as they have infant insert or sizeable base. This is important because it helps to keep baby's legs in the best position. For healthy hip and spine development.