there are online stores that have thicker carpets to reduce noise
Auto Carpet for Car, Truck, Van - Stock Interiors
there are also shps that specifucally sell the hush matt and sound deadener
Vehicle Sound Deadening Materials for Noise Reduction, and Thermal Insulation. Call 800 679-8511. | Second Skin Audio, Made in the USA.
and if you wanna make your exhaust quieter look into a good heavy resonator
you could look into undercoating, its not going to be significant but does help.