I would really shy away from MS 365 -- but that is just me. I don't like that whole subscription thing -- but a lot of "consumer advocates" in the media seem to agree with me.
There is no gold standard here. There are the usual bit torrent solutions, which are patently illegal, but seem to work for those who have the guts.
There was good outfit in Utah that offered discount Word etal, but they went out of business a year or so ago.
A google search will find you a few O.K. discount options, but they don't save you much. There will also be a few other options that save you a fair amount that sort of fall into the gray area....
I am not going to recommend any on a public forum, but if you want to go cheap, you can find them.
If you want rockk-solid 100 percent you will not run into any issues, you have to pony up the bucks to MS, unless you want to take the Open Office options as suggested already. That would be me route, if I were you, but, seriously, most "average Americans" will not want to make the effort.
So, get ready to write that check to MS>>>>But, if you do, I would suggest looking hard at other options before going for 365.