What do you mean by "simple": simple to setup, simple to run?
All Mac are relatively simple to run. However, the one piece, desktop Macs are the easiest to setup. However, they are more expansive that a Mac Mini with a 3rd party monitor.
Also, there's an open source, free app, LibreOffice , that can open, edit and save Word and MS documents in Word/MS format or its own format. It works with all systems.
Also seriously consider den.thed's #3 comment. It's should be your first consideration. Also do not buy from eBay, Craig's List or Amazon. Wherever you buy a second hand Mac make sure it's been prepared according to What to do before you sell, give away, or trade in your Mac - Apple Support and that you can return it for a full refund.
One vendor that I can recommend for refurbished Macs or new hardware is OWC (MacSales.com).
