In the case of the baby, I usually prefer that they're undressed for the occasion. Baby skin is a thing to celebrate, not conceal in bulky, distracting clothing so crank up the heat and show off that birthday suit. If you're worried about accidents on your bedding, try a chic diaper cover. I use Etsy or mamique. designs.
For you, dress in simple, uncomplicated clothing with colors that complement both your skin tones as well as your bed set. You want the focus to be on your baby and you, not your outfits.
Photo courtesy of: Nancy Alcott Photography