Assuming you're going down the completely legitimate MSO route, I am not aware of any way to own MS Office =>2013 without a Microsoft account.
I too avoid the Microsoft account requirement in Windows, which you can still do while successfully activating MSO. If you buy a boxed MSO product or an electronic-only transaction, you'll end up with a product key in either case. You then create a Microsoft account (I'd advise attaching it to your e-mail address), go to
www.office.com/setup, follow the steps such as signing in, put in your product key, then that licence will be attached to that MS account. That URL will take you through the rest of setup on that occasion, then in future if you need to re-download it, go to
www.office.com, sign in, go to either payments/order history (make sure you set the filter to show all transactions for all time) or active subscriptions (in my experience MS likes to take some steps to actively hide a standalone copy of MSO because they really want you to rent it), then it should list your copy of MSO to download. Beyond the first time, the product key should be superfluous (though I would keep hold of it).
When the installation program runs, it'll then want to activate with MS and your MS account. I believe then is the point to look out for the option of just signing into 'Microsoft apps only' which will ensure that you continue to sign into Windows with a local account.
I whole-heartedly recommend LibreOffice. Less hassle, less annoying integration, and in my experience works fine in terms of document compatibility. Where it comes unstuck in my experience is when someone uses say Word in an incompetent fashion (e.g. implementing 'centre align' by using the tab key repeatedly). LO can be set to save to modern MSO formats without you having to change the file type option every time, that's what I do on customers' computers.