Use LaTeX

For scientific writing, LaTeX is pretty much standard, and most theses and scientific articles are written with it.

There is a learning curve, as you need to understand some of the LaTeX language. However, there is also lots of help available on the web. For your needs, standard templates and styles should work quite well.

One of the benefits of LaTeX, apart from its high-quality output, is the fact that it uses normal text files as input, which simplifies version control and backup. You can for instance use Git both for taking care of incremental changes and as additional backup. You can also use any text editor of your choice.

Use Git

Git is a version control system that lets you keep a local copy of the repository, manage your commits locally and then also push it to other repositories. You can also tag different versions.

For writing, a nice aspect is that you can create commits for different portions of your work, so that you can also review your changes you made in a work session, similar to incremental work in programming.

A good practice is to start each sentence on a new line, so you can easily see changes in your work on a sentence level when you commit them.

Make Backups

Of course, make sufficiently backups of your work, both on-site and off-site.