With coilovers, don't you need new struts?
True coilovers have the struts built in, your thinking of coilover sleeves like ground control. Good coilovers are expensive, but its the ultimate in adjustablity and Performance. But remember if you keep adjusting the height your gonna have to keep gettin the tires aligned. I'd recommend tein, they have a good reputation and the quality of my s-tech springs is good.