I've posted about this before, but I used
this one. I had it on my Oasis 2 for at least six months, and it held perfectly. I could use it with two or even three fingers (I have small fingers) and it worked great. I liked the fact that the base was grey so it sort of blended in with the back of the Oasis.
I removed it from the Oasis 2 because I decided to use that one as my traveling Oasis when I got my KO3 and wanted it in the Amazon waterproof cover. The handle came off easily when I used an old plastic credit card to separate it from the back as recommended by the manufacturer. It didn't leave any residue or marks. Just for a whim I decided to try it immediately on my Oasis 3 (I'd already bought a brand new one for that Oasis) and amazingly it adhered well. So I'm keeping the new one as a backup should the old one loosen up.
For the person looking for a sleeve, I use
this one for my Oasis 3.