Yes - a GOOD staple gun. Last time I did it I made two trips to Home Depot. Tried two different electric staple guns.
Most Importantly -- get someone to help you. They can pull and hold while you staple.
Bend the seat a little, against the slope as you staple -- when you let it go back to its normal position it will stretch the cover.
TAKE YOUR TIME.
Worst case scenario -- you end up with a bubble -- THEN take it to an upolstery shop.