We sleep side to side in the overcab bed. I replaced our thermostat, which was mounted to the cabinet between the sink and the front (truck cab) end of the camper, with a manual garage thermostat that has settings down to 35 deg (search WTW for posts about doing this).
We have a warm double sleeping bag so I often set the thermostat for 50 deg or less at night. I oriented the thermostat so I can easily reach the lever control from the over cab bunk (not all thermostates can be mounted both vertical and horizontal). If it is too warm or too cold it is easy to reach down and adjust the temp lever slightly.
When I want to get up I can reach down from the overcab bed and flip the temp lever. Works pretty well for us. To be sure it would be much more convenient if it were mounted on the wall at the hight of the cabover bed but I did not want to pull the paneling to run wire to a different location higher up.
I hope this is of some help.
Craig