It depends on what you are doing.
If the documents you create don't need to be shared with Word... that is they go straight to print, PDF, or for your own internal use then I would say you just need Pages. It will allow you to read Word documents, and occasionally to edit or create a Word document. It won't always look the same... but it will be close enough for most uses. Keep in mind that a Word document can change it's formatting when being shared among Word users, if the version of Word they are using is different. And printing word processing document (Pages, or Word) can change the formatting if the printers used by two different people handle printing codes differently enough.
For a bit more Word compatibility there are some Word Clones. I use NeoOffice, and others recommend OpenOffice (or whatever it's called now - LibreOffice?).
You could always start with Pages and Keynote, and see if your workflow can cope with the Word limitations. You can always upgrade later, especially if you find a sale on Office somewhere.
Luck.