Newborn clothes size

I understand that baby grew up fast and its best to buy bigger size. But my MIL is insisting to buy newborn size and despite being told of my concern on baby size and fast growth she insist to have 12pcs of tie front newborn size so that baby will be comfy. I do not want to disrespect so ill do as she say while purchasing some bigger size to standby. but im confused to buy 52cm or 59cm newborn clothes as 0-3months is considered big to her too. #advicepls