GO TO TARGET , their sale starts today and there is a seat call HIPOD SENATOR , its an 8-26 kg booster seat , similar to maxi rider ...
it was an option for us and so was the maxi rider , but we ended up with a safe and sound HI LINER with an anti submarining clip as a maxi rider and the senator were way to wide/big for my car ...

If you have a small car try the seats in there first ... i have a rav 4 and they were just to bulky , a HI LINER is cheaper but its got a whatchamacallit thing .... the things that keep the seat attached to a car , anchor point !!!! so its safe but you do need an extra harness ...

hth