Winter Lullaby

A friend has asked for warmer clothes for her baby, like sweatshirt fleece. I've cut a top from a waffle knit and am wondering about making the pants from flannel. Any other tips? I have some pinwale cord but it's so light, I don't know that it would actually do much in the way of keeping her warm. I thought also of perhaps changing the placket to another, smaller kind of opening, maybe a keyhole with ribbons?