I would like to measure the temperature of a heating wire (tungsten) that's wrapped around my sample. Does anyone have a better idea than using a infrared thermometer, which has relatively low accuracy? The expected temperature will be between 200-400°C
If you can afford it, a thermal camera (e.g., FLIR) should do the job.
It determines the temperature of objects based on their infrared radiation.
There are plenty of models with different characteristics and features - you'll have to choose (buy, rent) a model, which will be optimal for your expected applications.
It would require some tuning and calibration to take into account emissivity of the wire, temperature range, etc., but, in the end, it'll give you a lot of useful information.