Analog gauges are highly inaccurate. You would be better off with something digital. I found the best thing for heat and humidity is a hygrotherm. You can hook your fogger up to it and your heat lamp and it will turn them on and off when it reaches the levels you set it to.
What type of bulb are you using right now, what is the wattage and what kind of fixture? As long as your fixture would allow the extra wattage, you could just go the next wattage up from what you are using.