I would suggest to move on 15's rims with atleast 70 profile.
Dunlop Sp 3000 (185 / 70 / R15) are really good tires and are easily available.
Packing would certainly disturb all your car's drive and pleasure.
Regarding harder springs, I used them in vitz and was not satisfied at all as they are locally made and sounds came from them after every rain, unless I get the car serviced with some diesel spray which I am very much against of.
Hope above helps