Yield- no idea, honestly.
A soil that resists changes in pH sounds like it would be right up your alley. IF you have access to a farm supply store that sells composted humus, this is a good soil ingredient. IT buffers the pH right where you want it for a soil grow. The farm supply, and even the home depot, around here sell a couple products that are appropriate. The one I prefer is a coarse mixture of composted cow manure and composted humus, whcih comes out of the bag at .5-.5-.5. Then I cut it by ~30% with perlite to drop the nutrient % and lighten it for drainage. You don't have Agway where you are I'll bet, but any farm supply should have something comparable.
Another option is ProMix BX or HP. This is a peat based, lime buffered, soilless mix that is often used in nurseries. If you use promix, you should plan to re-pot at least once every 6-8 weeks into a slightly larger pot, because the lime gets used up and the pH drops. Re-potting helps keep that from causing problems.
Take the clones from a healthy plant that is in veg. Take the top shoots closest to the lgiht. Wait until the plant is large enough to provide at least 4 healthy shoots, while still leaving about half the plant intact.