I have two of these in the back of my 997 and they fit pretty well. I have an almost 3 year old (yes, I know this means they are a 2 year old but they're nearer small 3 year old size!) and a 7 year old. Worth a look.
https://www.halfords.com/baby-and-c...ntials-group-1/2/3-child-car-seat-131670.html
https://www.halfords.com/baby-and-c...ntials-group-1/2/3-child-car-seat-131670.html