I got:

https://www.amazon.com/gp/product/B06XZF5LCQ for "normal" sized cards. (Events, Portals, Mysteries, et)

https://www.amazon.com/gp/product/B002QXW4M6 for "mini" sized cards. (Artifacts, Spells, Items, et)

https://www.amazon.com/gp/product/B08D8KHKPL for "large" sized cards. (Old Ones, Investigators)

These all worked out fairly well. They're not "tight" and the cards slide a tiny bit in the sleeves, but they shuffle together easily when I split a deck and push one half into the other along the long edge.

The case I bought was this:

https://brightbearlaser.com/games/eldritch-horror/

It looks like he might be out of business for now. I wouldn't highly recommend it as a case. Yes, it looks pretty cool. Assembling it was fun (do this quickly and in a controlled climate - the parts might warp over several days if you don't glue them together fast enough). The box itself is the only issue. It's fairly flimsy from the hinges and the handle. It all really feels like it's mostly for show - the leather is held on with tacks and feels like it would give out if I gave the handle a sharp jerk while holding it. The hinges use tiny nails. I suspect that with time I'll end up repairing both parts myself.

However, as a game case, it's fine. Just don't treat it like a suitcase. The card carriers all fit together in a very neat, clean arrangement that keeps everything exactly where it needs to be. It makes unpacking the game to play much easier as I can use the card carriers as card holders on the table.