I haven't received mine yet, but like you, I've been searching for options. Here are a few I'm trying to decide between various cases. Usually I buy a case rather than a sleeve, but I wonder if a sleeve would protect it better when not in use since it wouldn't let sand or dust onto the screen. I typically buy from Amazon or Aliexpress. Amazon is sometimes cheaper and a lot quicker with prime, but they don't have everything! And sometimes the item is exactly the same as the aliexpress one, but costs twice as much.
Good luck! I seem to remember big lots used to have some cheap ereader cases, I might give them a shot before ordering from online.
Here's some I've favorited.
WY 6 inch Sleeve Case for Kindle Paperwhite 6-Inch 7th/8th 2014 2016 Voyage e-reader Pouch for All-New Kindle Oasis E-Reader（Blue）
https://www.amazon.com/gp/product/B0...A3SZLDJ0V72DC3
No reviews, but I like the look of the color and how it zips up.
For Icarus Illumina E654BK 2016 Case PU Leather Cover 6" eReader Pouch Sleeve Protective free shipping with tracking
https://www.aliexpress.com/item/For-...308.0.0.Qhxy0v
I like the black one with gold decorations on it and it has elastic at the corners.
2016 all new kindle 8th generation cover case new ereader kindle touch screen 6'' cover case
https://www.aliexpress.com/item/2016...308.0.0.Qhxy0v
OMG Flamingos!!!! Although its for the all new kindle rather than the prime. It looks like the biggest difference is that the prime is thinner. Not expensive, so I might buy it just to test it out.
Slim Brief Case For Kindle 499/558/paperwhite/voyage Cover Bag For Kindle Paperwhite Protetive PU Leather 6 Inch Sleeves Shell
https://www.aliexpress.com/item/Slim...308.0.0.Qhxy0v
This one isn't enclosed, but I love the colors and its cheap.
Shockproof Portable Carry Bag e-Book Sleeve Pouch For Amazon Kindle Paperwhite/Kindle Voyage/New Kindle 6 inch Cases Protective
https://www.aliexpress.com/item/Shoc...308.0.0.Qhxy0v
This is a nice looking zippered case. Not fond of the fabrics though....
wholesal universal tablet case 5 6 7 8 8.4 inch android&kindle ebook Cover sleeve pouch bag for Teclast Pipo Lenovo Cube chuwi
https://www.aliexpress.com/item/Leat...308.0.0.Qhxy0v
There's something about the area under the envelope flap that I love on this one!