Several suggestions about the staples...
If you take a penknife and bend each staple leg back to it's original shape, sometimes you can re-use them. Or even leave them in the same holes for when you re-install the seat cover.
If you break the staples taking them off, you can find the same size at an upholstery shop or maybe a hardware store and put the new ones in the same holes. You only need a handful, sometimes a shop will just give them to you.
Depending on how much padding you add or remove, maybe you'll be able to use the same holes in the cover, too. If not, then just punch new holes as you stretch the cover over the staples. Then take a small hammer and bend/fold them back over flat.
Punching new holes may or may not weaken things, so I would re-use the old holes if I could.