I have a really bad back (surgery to repair it 25 years ago but even as I type this I'm sitting in a very nice chair that I have to use a lumbar pillow behind just to be able to sit for more then 20 minutes in) and the seats in the C-Max are fine, at least in front. They are the most comfortable I've had in ANY car (and that includes about a half-century of car/truck ownership).
But... I've never had a Volvo and I suspect you get used to certain things and it's hard to adjust. I have the base SE model and have no problem getting them comfortable for me (but with a bad back you should be aware that in most cases it's very important to have your legs MUCH closer than most people like to drive -- valets are always readjusing them just to be able to get in, since my legs are so bunched up and I sit so very close to the wheel).
I think experimentation is in order for you.