So, you're worried. Don't be. I worried the first seat I covered. The one on my HX. After I finished I was full of confidence. Just take your time, put the seat cover in the sun. Get it pliable. The biggest advice I can give you is staple in as far as you can. Flip, check, flip, check. Make sure it's lined to how you want it. Then I'll pop a staple, stretch the material and staple close to the edge where the original cover was stapled. Then go to the other side, same thing. Then the back, then the front. Flip, check, flip, check. If you like how tight the cover is and it's positioned correctly, staple in the original area and do like a 6" row of staples. Then the other side. Then back, then front. Flip check, flip, check. Just take your time. I'm always stretching and pulling the cover making sure it's tight to the foam. Once I start getting towards the tight corners I'll start to trim a little excess material if it's a bitch to work around. I remove a lot of staples in the corners when I'm trying to perfect the corners. As long as I don't see any wrinkles on the outside edges i'm not totally concerned with the underside as long as it doesn't look like crap. You can always go back and pull staples to pull it tighter. Then once you think you like it, start to trim the extra material back to where it's stapled.
The 4th pic. That's my starter staple, all the way in past the foam seat seal.
Seat covers..... Jet trim is probably hands down the best you'll get. The Black tip premium, second, they actually put foam on the underside like jet trim, really nice cover. Then you have just regular vinyl that's patterned or just a single piece of vinyl. If you wait till black Friday, black tip usually has a 50% of sale. That's where I got my one I pictured. I picked the colors and material. It's black suede and yellow carbon fiber vinyl with yellow thread. It's pretty damn nice.
Now, staples. Everyone is gonna say stainless. YES. Personally, I use the T-50 3/8" from home depot. Others will say, Oh, you have to use Monel stainless staples. Umm, no. I ride in fresh and salt water I've NEVER had the staples rust. Ironically, I have a seat from a 99SPX with the original cover and staples and there is a section with rust staples, Monel staples, from the factory. The one picture of the gray carbon fiber seat material is from my HX. I think I finished that 5 years ago ... No rust on those staples.
Staple gun. I use a pneumatic one from harbor freight. I think it was like $25. Best money I spent. I don't know how many seat covers its put on. Many seadoo covers and a slew of dirt bike seat covers.