Epsomsalt

I am in the throes of buying a 2018 ( reg April 2018) Audi Q3 1.4 S Line Auto. the car has a low boot floor I.e. carpet sits straight onto the floor, I would like to know if it can be converted to a higher floor to accommodate a foam insert to house a space saver spare tyre?? if so any idea of cost please?? Thanks Chris