In my 51 Clio i got 5.25" Sony Coaxials. 35w RMS each and was as simple as nefin to change, Pop the covers off, remove 4 screws disconnect the block and the quick rewire and Bingo! They do carry a far bit of bass considering there size. Got them from Halfrauds fot 30 quid so not exactly bank breaking.
Im tempted to try and alter the rear speake4rs to get some 6x9's in but again they are 5.25" and another easy fitting if just a replacement.