You'll have more room and be much more comfortable in case you're stuck in there during bad weather. Get an air mattress. It really sucks trying to sleep on rocks and twigs. Most times, people are prevented from enjoying camping because of bad sleeping conditions. But a good nights sleep in the woods will keep you going back for more.
Air mattresses come in every standard bed size.
Buy yourself an air pump for mattresses. They inflate a king size mattress in about 2 minutes. Unless you'll be camping in warm regions, you will need a sleeping bag. They are rated according temperature. You're best off buying sleeping bags that are rated for the extreme temperatures in the area you'll be camping.