For car camping you have a lot of options. Cabelas makes 2-3 inch-thick foam pads you can use on the ground or on a cot. They're inexpensive and light but a little bulky. If you stack two it's almost like sleeping on a bed. For lightweight packable pads that could do double-duty if you ever need to put them in a pack, look at Thermarest and Exped. They are more expensive and not really needed for car camping, just an option.
