Looking for a dual thermostat for a combination furnace
The simplest, and likely the most flexible is what you have already, is a two separate thermostat solution. The main reason is that you can locate the thermostats in two separate locations so that different factors in the dwelling can be taken into account for controlling the furnace unit.

Getting back to your specific question about a dual thermostat it would seem that a two zone thermostat may be what you want. These, and there a plethora of various types available, are normally used to control temperatures to different rooms or floors of a multi zone heating system. They should be able to control your dual fuel furnace as well just by not using the part of the system that controls zone valves or zone baffles.