Anything that can firmly hold the thermistor to as large a cell surface area as possible and increase the rate of heat transfer is good. Pressing it down between cells, firmly against both cells, is good and using hot glue can help transfer heat to the thermistor.
If I have to use a thermistor (instead of thermocouples) I like to embed the thermistor in a blob of thermal paste and press it firmly against the cell(s). It’s easier to force the paste into all the air spaces around the thermistor bead, it conducts heat better than other materials we can use, and cleans up fairly quickly.
Also tape down at least a cm or two of the thermistor wires to one of the cells as this helps keep the wires from sinking away any heat from the thermistor bead.
A lot depends on whether this is for testing or for a pack going to a client. If this is a permanent thermistor install for a client pack I would thermal epoxy the thermistor in place. Kapton tape over it to hold it in place and hold down the wires.
Hot glue can soften if the pack gets too warm and this could lead to the thermistor losing some of its already very limited contact with the cells.