We are currently looking at developing a dedicated thermocouple interface board around the Maxim MAX31856 which is a precision thermocouple to digital converter that would connect to the Raspberry Pi through the SPI bus. It supports K, J, N, R, S, T, E, and B type thermocouples and has internal cold-junction compensation which should increase the accuracy. We could add a single or dual channel ADC which would work with the TMP36 sensors.
The new board is still in the early prototyping stage at the moment. Some MAX31856 chips arrived from Maxim this morning so I need to build a test circuit and see if they will do what we need but if they do work then hopefully we can have a working board on sale within a couple of months.