Is the Book Armor still made? I have one which my old Sony 505 sits in. They're great for protecting ereaders from hard knocks. I'll quickly do a search and modify this reply depending on what I do/don't find.
Yes they're still made, here's the link to the main website:
http://www.ecaddycase.com/index.html
If the Oasis is the same size as the PaperWhite you'll need the Shield version. But I have a feeling the Oasis is smaller so buy the smallest case they sell and pad it. They really are excellent.
Failing that, I have one of these which I use as a secondary case over a very slim August make of cover on my Paperwhite. You can buy a red one on ebay if you don't like the colour:
https://www.amazon.co.uk/Belkin-Univ...+pleated+cover
This has a very useful pocket which I keep the usb cable in.