This site is cool, you can select your year and color combo and it gives you a sample view of what it looks like. You can also order door cards to match. I was looking at Black and Red covers to go with my Red Z. A little pricey but if you want to keep the same seats and just change the covers yourself this could be the way to go.
https://www.leatherseats.com/shop/le..._store=default
Youtube of seat covers installed on a 350Z
https://www.youtube.com/watch?v=HDtqLR5zQY8