Don't worry about not matching it perfectly- I have found as long as the organics(especially peat) are kept to a minimum they will thrive in a number of "airy" mixes. For my mesembs I go fairly simple: 2 parts pumice or small "pea" pebbles, 1 parts perlite, 1 part course silican sand(not beach or play sand) and just a dash of clay to help hold it all together. If it sets like concrete you put too much clay. I like to dress the top around the plant with rock to allow the plant to not set directly on the media; lithops especially as easy to rot. Hope this helps. :)