We have a V60 and have just discovered that, because the rear headrests aren't designed to come out, it is not possible to fit a stage 2-3 booster seat with back support - the headrest stops the back of the booster seat going flush against the back of the car seat.
Of course, you can buy Volvo's own...it costs 3 times as much as the ones we wanted, and comes in any colour you like as long as it's black. I would include a link, but it isn't on the Volvo cars website, you have to go through a Volvo dealer. But then, it's not as if there's any point comparing features with other booster seats when it's the only one you can buy anyway. GRRRRRRRRRRRRR.