Yes it does matter, you need to get the correct spring rate (normally denoted by the colours on the spring), as these need to match the others / match the dampers.
I very much doubt ECP will have the correct springs, they'll just give you a non-RS spring.
So your options are:
* @renaultpartsdirect
* Go to Renault directly
It might be worth getting dampers and top mounts depending on condition, as you have to take it all out anyways.
Dampers are on sale on RPD's site @ @£35 each, which is a bargain.
So you have a few options
* H&R Springs (biggest drop, in my opinion horrible ride)
* Eibach Springs (less of a drop, but progressive springs, so ride decent still yet on the limit a bit stiffer)
* Cooksport Springs (no experience on these, a few people do run them)
* Grams (again no experience with these)