Security threats to office suites are almost non-existent. I've NEVER heard of anyone suffering any problems due to attacks on Microsoft Office products. (There are millions of people still using Microsoft Office 2003, or earlier versions, with no problems whatsoever).
Microsoft's 'support' systems for much of their software seem to have little to do with helping to keep users safe and everything to do with persuading them to pay out money for 'upgrades' every so often. (Similarly, the move to use .docx, instead of .doc, as the default file format for Microsoft Word seems to have little to do with improving anything but a great deal to do with trying to render older versions of Word out of date).
So I doubt that you actually need to do anything at all.
However if you're seeking a safe, free alternative, there are three main candidates:
LibreOffice is popular with quite a few AB members:
https://www.libreoffice.org/
WPS Office 2016 Free (formerly Kingsoft Office Free) is less well-known but, just like LibreOffice, gets good reviews in the technical press:
https://www.wps.com/office-free
However, far more well-known and popular than either of them is the excellent Apache OpenOffice, which is used by lots of ABers (including me) and is also being adopted by many businesses and public bodies who are fed up with forking out money to Microsoft:
https://www.openoffice.org/
In your situation I'd either just keep on using Microsoft Office 2007 or switch to OpenOffice. If you do choose to use OpenOffice though it's worth noting that the default 'Save' options within it use different file formats to Microsoft ones. You can get around that by remembering to use 'Save As' (instead of 'Save') and choosing a Microsoft file format but it's probably better to change the default settings to automatically use Microsoft formats anyway. To do so simply follow the easy instructions here:
http://helpdeskgeek.com/office-tips/set-openof%EF%AC%81ce-org-to-save-in-microsoft-of%EF%AC%81ce-format-by-default/