Top recommended thermometer is the Acurite which measures in/out/humidity with one unit. The probe would go under the warm side hide (the hide keeps it basically in place) nestled under the substrate against the bottom. The unit usually gets placed on the other side on the back wall on or near the bottom.

Other options for thermometer would include the Exo Terra digitals with probes, or basically any good digital unit.

As for thermostats, they ALL have sensors because that's how they tell what temperature the surface is at. You place the stat probe outside the enclosure right against the heat source. I use foil tape to tape my stat probe under the tank right to the UTH.