What does a newborn need?  Baggies, Blankets, Topee, Diapers - lots of love and cuddling.  For daytime when the infant is just being cute in their crib, a diaper and a long or short sleeved tee or a kimono is great if their room is reasonably warm - above 70 degrees.  If you are comfortable in a short sleeved shirt, they probably are too - don't make them so warm their cheeks get red - they are little metabolism factories.