American Airlines way back had "more room" seats which were only slightly more expensive. I loved it and became loyal. But then they stopped. I guess not a lot of people wanted to pay the few bucks.
They still have those seats; they're branded as "Main Cabin Extra". They're not super expensive, but the price will vary depending on the perceived desirability of the specific seat you select (i.e., an extra-legroom middle seat probably doesn't cost as much as an extra-legroom aisle).
Most airlines also build free or discounted access to those seats into their frequent-flyer perks, though Delta has recently begun cutting back hard on that and treating it as a possible-but-not-guaranteed after-booking "upgrade" even for their top-tier customers.
Most airlines also build free or discounted access to those seats into their frequent-flyer perks, though Delta has recently begun cutting back hard on that and treating it as a possible-but-not-guaranteed after-booking "upgrade" even for their top-tier customers.