I had a 350z and I thought they were some of the most comfortable seats ever. I could drive for hours and hours and it always felt really supported.
I read up lots about a 370z and everyone was saying they seats were uncomfortable (compared to a 350z) and I certainly noticed the difference, I found them uncomfortable at first. However, I've played around with the seat so many times and I've got it about right.
Something that may help you.... When I was trying to get the seat right, I discovered a small lever half way down the side of the seat (so to the left of your chest) and turing this level increases/decreases the support right in the middle. If it's fully turned then it can feel like something is digging in your back and then if it's turned the other way that's when I felt it didn't offer enough support.
My lever is pointing upwards and towards the windscreen. if you looked at it from the passenger seat, it would be between 10 and 11.
Give that a go and see if it helps.