I have a Koaloha KSM-03, which is a super soprano pineapple - so this might not apply to the super soprano figure-8, not sure. Mine is 22" long and has a strap button, and I was surprised to find that it fit perfectly in my Kamaka HP-1 soprano pineapple case.
When I had a Koaloha figure-8 soprano years ago, I actually had more trouble finding a case to fit that because the Koaloha lower bout is wider than many sopranos. So keep the width in mind too, when checking dimensions.
One suggestion - call HMS and ask what case they'd recommend. They have a Koaloha figure-8 super soprano in stock right now, according to their website.