Airlines have devoted years of research and tens of millions of dollars to finding the perfect seat, CBS News correspondent Kris Van Cleave reports. 

Spirit's new seats have memory foam and a curved back so passengers sit further back. The airline also moved the location of the seat-back pocket higher. Though the rows are still just 28 inches apart, Spirit said the changes have freed up two inches of useable space. 

Spirit also said it increased the width of the middle seat by an inch, to 18 inches. 

"I think this is an amazing seat for Spirit," said Lania Rittenhouse, who spent more than a year fine-tuning the new cabin with particular emphasis on the seats. "The number of seats are still at 182. What did change was the livable space in the seat." 

The new seats are already on one plane in operation and will be on every new one. 

Alaska Air also has new seats that use memory foam. Created by BMW's Designworks, they are intended to feel a bit like a luxury car. "The memory foam was basically to give the guest a more comfortable feeling," said Molly Evans, creative director at Designworks.

Jetblue also went with a curved back seat with memory foam. The distance between rows will stay the same, but because the seats themselves take up less space, the airline can to add up to 12 more.

"It's incredibly important that we get this right because aircraft interiors do fly for a long time. So we put a lot of thought into designing what we believe is the perfect seat," said Elizabeth Windram, JetBlue Airlines marketing vice president.

The changes come as the Federal Aviation Administration is under pressure from Congress to finish testing to determine the safe minimum size for airline seats. Critics worry those findings could lead to even more cramped cabins.

"We think that the airline industry is looking at that report as a green light to cram even more consumers into ever smaller seats," said John Breyault with the National Consumer League.

New seats are typically lighter, which saves the airline fuel, and thus money, but they are still a multi-million dollar undertaking. 

"Believe it or not, airlines actually want us to be comfortable," said industry analyst Henry Harteveldt. "If the seat is a bad seat, if the customer isn't comfortable, they're going to remember that, and they won't choose that airline again."