Ladyearth, the warmers are available. Just the 7" tall one is expensive. The 4"' ones are definitely better than nothing. Look for "Heating Systems" at kombuchakamp. Like FoodFreedomNow said, it does need to be black or green plain tea. I use 3 Choice Premium Japanese organic green teabags, and 2 of some kind of organic black tea. Some people use loose tea; it is less expensive. But I don't care, I'm saving so much by brewing it myself.
I have seen the recommendations to brew in the bowls. That's to have more surface area, which is supposed to be better. But I've always used the glass gallon jars just because in my kitchen, something would probably fall in to that surface area. The jars have a smaller footprint and so far it has worked fine. Like foodfreedomnow said, it's important to have it at the right temperature (72-74 Fahrenheit is my preference) and use a lot of starter from the previous batch, or from your scoby hotel. Or even add a couple tablespoons vinegar to make sure it is acidic enough.
Foodfreedomnow, please update on how the continuous brew goes.