Plain old potting soil with perlite plus orchid bark or coconut husk chips works well. An 8" clay pot sounds like a good size because clay pots allow the potting mix to dry faster than plastic so a little extra room should not be a problem. When you allow a plant to stay in very old mix it usually suffers from nutrient deficiencies so I would recommend using a dilute fertilizer to water the plant as well.

Mike

I'm using Miracle-Gro for Orchids for all my hoyas. They seem to be doing very well in it.

I've been using a mix of equal parts decomposed granite, fine pine bark, pearlite, and potting soil. They seem to like it, as do my other areoids.

Our Jose-before we made the mistake of not repeotting him when he needed it LOVED African Violet potting soil mixed with a bit of cactus mix. Jose 2.0- a cutting I got from Jose before we lost him completely LOVES this same mix. I don't even need to feed though in the past Jose loved African violet food before I found this potting soil. He flowered just about every spring. Sometimes even in the fall.
Jose was over 40 years old when we lost him this winter.