if your going down the turbo route you will need to look at strenghing the whole engine.
shorter forged conrods to lower the compression, forged crank.
can the liners be bored ?
you might be better swapping out the 1.5 for another engine. do you get the mazda 3 in the US it comes with a 2.3 turbo ? or even a 2.0 would give you a better base to start from ( think the mazda 2.0s give around 140 bhp to start with ).
just remember to uprate the brakes and suspension to take the new weight