I use two vivosun digital heat mat thermostats (the ones shown here: https://www.amazon.com/VIVOSUN-Therm.../dp/B015F4VFGI)
The probes are directly under the hides, beneath the substrate.
I use these thermometers: https://www.petsmart.com/fish/heatin...ml?cgid=300121
And this hygrometer: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1