Lost installation disc

[Azure2011]

So I'm about to upgraded my 2009 iMac HD to a 1 TB Seagate Barracuda but apparently I lost my installation disc. If I buy the Yosemite, will it be as easy as installing the OS or do I need anything form the first installation disc that came with the Mac?

 

[Nermal]

The free download from the App Store includes the full OS. It does not, however, include the "iLife" apps such as iMovie.