Battery temperature charging cutoff protection methods
When I've designed battery packs we've always used thermistors to monitor the centre of the pack of cells.
Thermistors are easier and often cheaper than thermocouples to get hold of. Thermocouples are tricky things to measure, as you need to start doing cold junction compensation when you have a junction of different metals. Then you are measuring down the the uV range. Tricky do to cheaply and easily.
My BMS designs use a thermistor (NTC) plugged into a standard microcontroller's ADC. The micro controller then turns the charging FET on or off. This is the cheapest way to we found to make charging li-ion packs safe.
We have also done it with various Battery monitoring ICs, which often have a dedicated FET output (different ones have high side or low side drivers for charging and discharging set ups) and dedicated NTC (thermistor) inputs. So it's all there ready for you, just need to add the FET and NTC.
You talk about it as though it's a nice to have, if you plan to sell this product in the EU or US, you'll need more protection than just this (I believe the UL regulation for the US basically means you need to have two separate FETs which can isolate the pack during charging). Charging a li-ion pack is a dangerous thing: they can explode if handled badly. Please make sure you have proper control of the charging and discharging of the pack.