Re: sprinter seats from coversion companies
I think the comfort of our 2013 Sprinter seats is fine. I don't think that they are any different than your 2012 ones. We talked with another couple who had an older Sprinter based Roadtrek, and they said that the seats didn't move. (Ours spin around, go forward and backward, give lumbar support, and tilt back.) They also said that the visors didn't move to the side windows. Our 2013 is the first Sprinter I've owned and other than the other new ones we test drove, it is the first one we've driven, so we don't know about the history of accessories on Sprinters, other than at one time they had 5 cilinders and got better gas mileage.
Different people like different things, but my wife and I seem to like the comfort of the seats just fine.