I disagree, comfortable seat design applies to all. Anyone will be more comfortable on a seat with back recline.
On this forum people mainly seem to discuss the base and its padding, or lack of it. But IMO the single most important factor in seat comfort is the angle of the base and back. For me the IET seats are extremely uncomfortable because the back is almost completely vertical, no recline whatsoever, and this does my back in. I find train seats hard to tolerate for any longer than 45 minutes or so. And its the same on all trains. In a months time I'll be trying first class on GWR, London to Falmouth, hopefully the 1st class seats will make the journey tolerable.
I've got a wooden bench at home, its got a well contoured seat and the back is sufficiently reclined, this makes it comfortable to sit on for ages, more comfortable than a train seat i reckon.