Note that you can compare to versions of a document, one a "descendant" of the other to view its differences. "Track changes" feature may makes this easier for you, though. You can have the changes hidden when you are simply editing.
As for a better option, I would probably use a source control version system (svn, git…). They are really good at keeping track of what changes. These are normally used for computer programs source code but they will work with any type of files. If the file format is not text-based (such as writing the document in LaTeX), you will miss some features (e.g. you will be opening an external program for each comparison, you won't be able to easily view when was a change made...) as it will be versioning an opaque file an opaque file, but the basic features of saving multiple versions, that you can then compare between will be there.