I haven't actually got a seven yet, but......
When I test drove a seven with the leather seats they gave me instant back ache. For me, there was no lumbar support at all. As Petrohead suggested, I would try using something as lumbar support. I hope you manage to get round this :)
For my back the composite seats seemed much better, but as I haven't sat in them for more than a few minutes I'm keeping my fingers crossed they turn out OK.