The hardest wearing timber floor finish as used by most proffesional floor finishers is called "Moisture-Cure Polyurethane". Altho it's primarily an industrial product you'll find it at most good paint or hardware stores in flat, satin or gloss. 3 coats is normal butI would suggest 4 coats on high traffic areas like stairs.
It's a little harder to use than normal and smells terrible but will outlast normal poly finishs by miles.
To keep the color as light as possible ask for a timber sealer that is OK on oak and under Moisture Cure Poly. The sealer stops the polyurethane from absorbing into the grain maintaning a more natural tone.