Can I use an infant head support? Is it OK to put a padded cushion under the child for comfort?
Generally, NO. Unless such items come with the carseat or are recommended by the manufacturer of the carseat as an accessory, do not use them. Aftermarket pads and cushions are not tested with the seat and any compressible material inside the harness may allow for more slack in the restraint. With a small infant, it is usually OK to put a rolled towel or receiving blanket along the sides of the head (outside the harness straps) to keep it upright. You may also put a rolled towel between a small infant and the crotch strap if there is a large gap, though you should never put towels or pads under a child in a carseat.