The Mini Cooper has a small boot: 210 L behind the rear seats on the 3-door petrol. The petrol F66 and the electric J01 are built on different platforms with slightly different boot shapes, so always match an organiser to the powertrain, not the trim badge, and measure the floor before you order.
Three products we would look at first in this category. Fit for your Mini still comes first: check the compatibility list on the listing against your exact model and year, and read the model guide above.