If you buy a new Seagate HDD that will hold the clone copy, go to the Seagate website and download their free utility, Disk Wizard. (It appears to be a customized version of Acronis True Image.) It will do a LOT of jobs well (not just cloning) so get the manual and read it. BUT it is limited to making a clone TO only a Seagate product (they don't care whose old drive you have).http://www.seagate.com/www/en-us/support/downloads/discwizard
On the other hand, if you get a WD new HDD, go to their website and download their free version of the same thing, called Acronis True Image WD Edition.
Other HDD makers may have similar free cloning utilities to make it easy for you to buy and use their units.