Here's something I found works for me on long road trips. I take my wallet out of my back pocket and put it in the center console. I noticed a big improvement during one road trip and have stuck with it ever since. It seems obvious that sitting with a big lump under one butt cheek and nothing under the other butt cheek is going to twist your spine. However, this certainly does not explain why the new seats aren't as comfortable as the old seats.
Maybe another thing is whether the seats are MBTex or leather. I've had leather for many years and this time I switched to MBTex after hearing it was very durable. But it didn't occur to me that they wouldn't be as comfortable as leather. I've only had my car for a couple of weeks, so I hope I'm not disappointed.