Cryogenic PCB temperature monitoring
Lakeshore Cryotronics is one of the main worldwide sources of cryogenic temperature sensors. They have relatively inexpensive silicon diode sensors DT-670 that work fine for rough accuracy. I've used those and the Germanium temperature sensors (which are much more expensive and accurate but require specialized circuitry (AC energization at very low current and 4-wire measurements). The latter also come with individual calibration curve constants fit to the individual response of each sensor serial number. You might possibly re-think "price is not a problem" when you see the price list of instruments and sensors. 

In both cases I've designed circuitry to provide signal conditioning. In the latter case we were able to do much better than 2\$\mu\text K/\sqrt{\text {Hz}}\$ using DSP techniques and some very precise and stable circuitry, in an airborne instrument. The Ge types are more suited for lower temperatures, they are very nonlinear and give best resolution below 10K.  

65K might be a bit low for regular silicon diodes (carrier freeze out effects might show up at sub 100K) but you could probably calibrate thin film Pt1000 elements using a calibrated reference sensor.