The best alternative to MS Office that I have found other than the free LibreOffice or Open Office, is SoftMaker Office. They have a free version you can try out and also several pay versions. Download their trial version and try it out for awhile. It's fully functional for 30 days. I found it to be a very good alternative to MS Office. And it's 64 bit so it will continue to work after Mojave.
I downloaded SoftMaker Office and have given it a brief try. Seems pretty good. At least one glitch, however. I opened a Microsoft Word file that I had prepared some time ago. In addition to text (9 total pages), it had MS Word tables and some graphs (scatter plots created in another program) and a couple of pictures copied from the web. TextMaker 2018 opened the Word document with correct formatting (including all tables), and imported the two pictures that I had copied from the web, but did not import the graphs. In place of the graphs, there were blank spaces of the size of the missing graphs. The text below the missing graphs was in the right place on the page in all cases, but the graphs were missing. Curiously, I went back to the original program that generated the plots (Kaleidagraph from Synergy Software), and was able to copy them correctly into a blank TextMaker document. And I was able to resize them without distortion within the TextMaker document. The graphs, now within any of the SoftMaker modules, could be copied and pasted into Word or PowerPoint.
The reverse operation did not work: the graph, now in PowerPoint (or Word), could not be then selected and copied into any of the SoftMaker modules. No error messages -- nothing happens upon Paste.
I encountered no such compatibility issue with moving these plots between Word (or PowerPoint) and Apple's Pages or Keynote.
Makes me wonder what the MS products are doing to a graphical object when it is within a document (still using Office 14.7.2). I may contact the Softmaker developers to see what they have to say about this.
The spreadsheet module (called PlanMaker) was able to open a MS Excel workbook that had multiple worksheets, and all worksheets were present, including formatting (coloring of cells, etc.) and formulas. Regions of data in the Excel worksheets that had been previously selected (and never deselected prior to saving and closing) were also selected upon opening in PlanMaker.
Based on my brief exposure to this, it looks like the SoftMaker modules could be a very viable option to MSO if/when I decide to make a change.