Yes, buy the blue antifreeze from BMW. One is all you will need to replace the one that you have now. also mix it with distilled water. There is a good write up at www.pelicanparts.com
. go to their technical articles section.
You should also know if your water pump has the plastic or metal impellers. if you don't know and have the dough, then I suggest you change it. And while you doing that, then also upgrade to the aluminum thermostat housing which is prone to breaking. check all of your radiator hoses and radiator for leaks. and if you feel like also remember to change the radiator cap. always remember to bleed the system.
I know it may seem like a total overhaul, but just letting you know of things you may want to watch out for. You don't just want to change one thing and having something else creep up on you.