I think the general school of thought is to leave the cab uninsulated, and put a barrier between the cab and the back of the vehicle. Metal, wood, blankets, drapes, reflectix, whatever you choose to keep it separate from where you are.
This is mainly due to difficulty in fully insulating the cab. The main limitations are going to be the floor, the doors, and the glass.
The glass you can put up reflectix/temporarily black them out when parked, which can help considerably. However you will still have the bridge of the exposed door frame and A-pillar bringing in unwanted temperature change.
For the doors, the lower part needs to have room for the windows as they are rolled down, and most likely the interior door trim, so you will have about 1/4 inch of space to insulate, which isn't much. You can prevent bridges and drafts, but that is about it. You could also choose to hang a wool blanket or other material, blocking off the entire door, but again it will have limited effectiveness.
As for the floor, you have some room to insulate, however the dogbox over the transmission/engine needs room to be pulled back, so you cannot have thick insulation all the way to the edge. You also have the plastic trim in the footwells to deal with. Again temporary thermal mass (blankets, etc) can be used to prevent what you can, but the effort vs results is not going to be great.
So this is why most people cover their front windows, and let the cab suffer its own fate while you put up a barrier between the living area and the cab.