Camera Labs

Hi all,
I searched a lot in internet but i couldn't find an answer, so I hope you will help me with my problem. I have an economic manfrotto tripod with a small ball head that wasn't provided with a quick release system. I tried a friend's quick release and I find it very useful. I think I don't need a bigger head for my camera so I'm looking for the quick release plate only. I don't know what I have to buy; I found adapters and quick release plates, which one do I need? My plate is round shaped, not hexagonal, is this a problem? Which informations should I study in addition to the size of the screw?
Thanks in advance...