Here's another person riding in on a high horse...
Your "base document" should be a Word template rather than a document.

With a template, Word automatically creates a new document, based on the template, for you to use. When saved, it will not overwrite your document. Templates in Microsoft Word

If you've been using Word for years, it is about time you learned to use it. You may want to start here:
Basic Concepts of Microsoft Word - from Shauna Kelly

[With the exception of Office 365 being used online,] Word does NOT have an autosave feature that overwrites your existing document. It can save a backup every time you save your document. It can also save a recoverable version if Word is ended without your work being saved. Turning these on or off will not change what you are apparently seeing.

See Automatically backup Word documents for more on this. If you are getting automatic saves overwriting your document, something other than Word, itself, is in action.

You will not get a different answer elsewhere.