There are as many mixes as growers...not to mention that everyone sais has the best mix. It might be surprising but in part is true! Why? because the cactus, in general, don't care much about the soil mix....as long as they have some nutrient inside. I use to grow them well in regular potting soil and sand, about one part of each. You can also try the mix that they have in the garden centers or just take some soil from your garden and mixed up with course sand. For seeds just use a fine sand. If you live in a colder climate, like i had, just give them colder temp 4-8C (do the math for F) and decent light (not intense) during winter time. Also you have to stop watering! I use to water them 2 or 3 times from oct. to march and they use to shrink to half in size. With the first watering in the spring and the outside in full sun placing, they would come back to size and flower in a few weeks. It is nothing dificult, you just have to remember that during the winter, if the soil is moist the evaporation is slower in the cool conditions and it may lead to root rot if the soil humidity persists for a week or 2. It helps to use clay unglazed pots since they loose water easyer.
hope this helps!