I think the Elaine size would work with CDs. But it depends on how many you carry. If it were one or two, it would be fine. AIOs would proabbly be better too. But thats if you don't pack a lot of other stuff too.
If you just have a small wet bag; I would def. go for the vinyl inside.
I got the tie closure because I can "fill it up" more; I've had bags with all the different closures and I find the button and tie to have the most give.
I found that I can put everything I had in my XL ISM in the Elaine size and it fits fine; not protruding sides or overstuffed look.