Alaska airlines recently did a seat-redesign to seats that don't recline, but supposedly have ergonomic improvements. The in-seat cards advertise that the designs are by Recaro (a well-known premium baby car-seat maker).

Didn't seem to make much difference at all: the biggest variance was still absolute space: the "premium economy" seats were no worse, the non-premium economy were no better. As someone with both lower back pain (a slight recline helps a lot) and long legs (the person in front bumps me) it was pretty much a wash.