We have the instrumentation that can help you measure extreme cold temperatures, with high resolution to within 0.001 K, where sensor resolution permits.
And with our line of Scientific Instruments silicon diodes, you can hover fairly close to absolute zero, down to 1.5 K with a repeatability of 10mK @ 4.2 K. Also, do take a close look at the tiny Ruthenium Oxide Sensors. They offer excellent performance characteristics in magnetic field environments. These sensors do not exhibit magnetoresistance in fields up to 2 T over their range.
We also propose a complete family of cryogenic valves from Rotarex, three of which can be used down to 3.15 K (-270°C)