My impression when I started growing succulents is that everybody who's been doing it for awhile has a different "recipe."

After looking at about a dozen of said recipes, I came to the conclusion that everybody seems to use a volcanic glass for drainage, some organic matter to retain water, and sand or fine gravel for the delicate roots, even if the exact ingredients and ratios differ.

I thus used a mixture very similar to yours (with copra instead of bark). I used a ratio of 1:1 copra/perlite on the bottom two thirds, and 1:1:1 copra/perlite/sand on the top third. I'd probably use less sand in the future, but my little cactilings seem to be doing very well so far.