I just put a sleeper on my baby, so she would be warm. I've put a onesie on under it before, but right now it's just her skin. Is it better to have a onesie on underneath? I don't want her to overheat or something, her back has been a little damp before when I've taken it off w/ or w/o the onesie. Her little feet, hands, & nose feel very cold if she doesn't have on something heavy. Is there a "middle solution?"