Buy another drive.
If you are cloning your current drive and it dies during the process you'll have destroyed your backup at your moment of need. So buy another drive and put them into an every other week rotation.
You're right. But my computer has only 4 drive bays. I have the C: drive, a C: clone, a data drive only for my pictures, and a backup drive for that. I have several external drives, and one of them will be an image backup of my C: drive so that if something happens to the C: and the C: clone, I can do a Restore from the external drive.