No such thing as Future Proof. 5 to 8 years, is a long time in Computer terms, although many of us have PC's that are that old, it is usually because we are too miserable to buy a new one.
Buy the best you can afford. It will be past it in a year but you should get another 5 years, or so, out of it. Think of using Libre Office, it's free, and compatible with MS Office.