MS Office

You either single-purchase Office 2019 for Mac, or sign-up for Office365 and continue to get Office 2016/2019 for Mac updates. Office 2016/2019 for Mac are 64-bit application suites. That is your remedy for the Fall release of macOS.next.

As long as your OS is Mojave, don't worry. Your version of Office won't work with the following OS. If a new OS is released, you have the choice: or buying a 64-bit version of MS Office or not upgrading Mojave

It needs to be kept in mind that there are known problems running versions of office earlier than Office 2016 on Mojave. Also, Microsoft no longer supports any version of Office for Mac older than Office 2016. The 64 bit requirement of future macOS versions would be a less critical issue than the fact older versions already don't work well.

Microsoft Help Community

Or the free Libre Office is 64 bit...

https://www.libreoffice.org