I think it was likespace who said it best. Cheesemaking is all about managing the subtleties. Temperature control is one of those things that sounds easy, but is really really hard.
I started off (and am currently doing with my new system), by just using a pot of water as a double boiler. I used water inside my vat as practice.
Try to maintain a specific temp. like 153 deg. (not 152, not 154). Its not easy, but it can be done.
Then, try to maintain a specific temperature change. like 2deg over 5 min, or 3 degrees over 5 min.
Work on your technique with water first. That way, when you over shoot, or fail to raise 3 deg in 5 min. you only risk some water.
Its funny how the simplest things are the hardest part of cheesemaking.
When you master this, then its off to pH, then humidity, then cave temp.. (it never really stops.....)
good luck...