I was also thinking of changing my springs.
and after making a thread on here to discuss it.
I ended up changing my mind and going for coil-overs.
it is too much for me to type out again so il will just link the thread!
I hope it helps.
the part you really need to think about is the fact that you could actually end up with your car riding higher than you started!!
because, depending on the age your car it could have already dropped quite a lot!