I don’t know anything about Yogurt and it’s manufacturing process, nor do I know what a home yogurt maker would consist of. I assume that the main ingredient of yogurt – milk or some derivative (milk-fat, cream, etc…) is possibly essential to the process, and trying to substitute something else might be one reason for your non-success in the past.
What I do know is that my wife sometimes works for Norman’s Dairy marketing their Greek Yogurts. They are some of the nicest people I know. I have spoken to their food scientists in the past when my wife had questions about the ingredients or manufacturing process. I suggest you reach out to them either through their website contact form, or their facebook page. Helping you with some tips is not really going to hurt their business, so they might be willing to help.
No guarantees but it can’t hurt.
If all you need is a cheerleader, then by all means – “If at first you don’t succeed, try, try again.” Of course the double ‘Try, Try’ seems to indicate that another failure might be expected in between…