I like Clen, but I know what you mean with the feeling, you don't want to overdo it. I have used t-3 and some t-3/t-2 blends. I wasn't too terribly impressed with the thyriod supps, plus the chance for thyriod atrophy wasn't somethin I wanted to mess with too much for minimal gains.
One thing I would definitely check out is Yerba Matte tea, that stuff is awesome. I drink 3-4 cups of that a day and it really keeps me goin, great workouts on that too. I prefer it over clen because it doesn't give a jittery Clen or Caffiene buzz, more of a long strong even energy boost that doesn't give you heart palpatations and the shakes.
Another thing you might check out is Dermacrine, This stuff is supposed to have metabolism boosting effects with the DHEA in it and some mild AI and Pregnenalone (which converts to Progestorone) in it to keep DHT and Estrogen balanced. They tout big DHEA increases and some test increase too, both of which will help metabollism. This prod is supposed to be pretty mild on the system too.
I would still use the Clen, it's effective stuff, but I would try it with the above and keep the clen doses minimal so you don't get the shakes too bad (don't want to wreck your car).
-DMac