The most expensive bundle in Southwest's new fare program will be Choice Extra, which will also include the most add-ons as part of the base fare. Choice Extra ticketholders will get early boarding, two free checked bags and complimentary access to extra legroom seats at booking and complimentary internet.

With a Basic plane ticket, Southwest assigns a seat at the back of the plane, which is assigned at check-in. Also, flyers with that fare type will be the last to board the plane.

Over the rest of the year, all aircraft in Southwest’s fleet will be retrofitted to accommodate the new seats with up to 5 inches of expanded legroom, the company said in a statement.