This is what i have been installing in my project vehicles for sides and roof. I am using the non foil version for under carpet Second Skin Heat Wave Pro – Jute with Reinforced Foil – Headliner and Under Carpet Insulation (3/8" Thick, 24 Sq Ft - 1 Sheet) https://a.co/hbbQLCe
I helps my cooling...
Can you find some vehicles that are 30 or more years old with leather flooring? I would look at some at a salvage yard and pull the leather up and see if there is any damage. You might be able to find perforated leather as an option(would breath more. I know leather can do some insulating but...
You just want to make sure what you put down can breath. When i lived in a hot dry climate, it was very popular to remove the carpet and put down rubber or vinyl. The idea was that it is easier to clean... Well it attracted the moisture from the people breathing and any condensation due to temp...