No suggestions for the interior walls.
But improvements can be easily made for some other areas for more comfortable cold camping. I've found that combining several approaches that individually make small improvements can add up to a much better cold weather camping experience in a pop-top and also lessen your fuel consumption rate for heating.
I'd say first is to add the inner liner to the pop top roof canvas. I've got the FWC inner liner, and it makes a noticeable difference. Others have done a custom approach using various materials ranging from fabric, wool blanket sections, Reflectix. The insulating air space helps for both heat retention and reduces condensation.
Second would be to address the sleeping overhang platform area and aim for both cold insulation and moisture ventilation. A DenDry pad or similar "air weave pad" product is commonly used. You will notice the improvement the first night with just the DenDry. You can also add a 1/2" closed cell foam pad on top of the DenDry. Together these will only add an inch to your bedding system so you should still be able to close the roof without removing the bedding.
Third will be to address the windows. Simple cut outs of Reflectix or insulating foam board covering the single pane glass on major windows will help a lot. To keep the interior suitably ventilated to reduce condensation crack a roof vent and one of the turnbuckle doors.
Fourth is the floor. Adding foam board insulation externally between the floor risers is easy. We also have a floormat "carpet" for our Hawk floor. Got it from Lowes, cut it to fit. Easy to keep clean, can be hosed off and dries quickly in the sun. Very comfortable on the feet.