I would ask your niece what she would like you to buy, rather than giving her something which we remember from long ago which is now old fashioned. I remember those vests, cosy but what a pain the ribbons were. Times change. Maybe a voucher would be a good idea rather than foisting your choice on her, if she won't say exactly what she'd like? Personally, that's the way I would go so that the new Mum can choose for herself.