I just had to top up my radiator with coolant as i noticed the car was starting to overheat today

Should i be worried about a crack in the radiator or leaking pipework?
Also what kind of coolant should i be putting in? The car is due in for a service in 2-300 k's so i will probably get the mechanic to look at it then, though should i be doing anything now? I'll definately be keeping an eye on the coolant levels over the next couple of weeks (everyday).
Cheers