Hi BobsChick! I fly every other week out of Atlanta to various destinations around the United States (for business). Atlanta is a hub for Delta and AirTran. Therefore, if you are able to fly out of Atlanta, you will surely find a better deal then flying out of TN. However, if you are unable to fly out of Atlanta, I would still recommend checking out Delta and AirTran.
When I make reservations, I use expedia.com. Expedia.com allows you to search for the cheapest flights on many, many airlines. You can book your flights with a credit card, and Expedia will issue you an e-ticket. There's no paper with an e-ticket. With the e-ticket, you just walk up to the check-in counter, tell them you have a flight to Orlando, show them your driver's license, and check any bags that you want to check. They'll ask you some routine security questions. Then, you'll be issued a boarding pass with your seat assignment. You go to your gate through security, board the plane, and your off to WDW!!!! It's super easy!
You should look for tickets to Orlando ASAP. Generally, the sooner you're able to reserve your tickets, the cheaper they will be. The longer you wait, the more expensive they will get.
Please let me know if you have any questions! Have a great trip and a safe flight!