While free is a big word in use these days, some things are more free than others. Open source and Libre in software grant complete freedom.
Using styles in your documents can save you lots of time and lead to more consistent formatting and presentation. A brief introduction to the idea.
Are you being forced to upgrade your office suite again to keep up with newer computers? LibreOffice has all you need and it’s free.
Moving from replacing items of regularly or less-used software to Open Source versions can be a big step. Switching operating system is entirely another.
If you want a photo editor with lots of power for your (no) money, then GIMP should definitely be on your shopping list.
Audacity sound editing and recording. If you’re not a professional that knows the name of the software you want, then this will have all you will ever need.