I chose Summit sound pads, rubbery stick on w aluminum outside layer, smooth it with a steel roller (or deep socket)

https://www.summitracing.com/parts/sum-879020?rrec=true

Peel & stick, one kit was enough for firewall, floors, inside doors, and some behind the seat, still a little left

Put the stock rubber floor mat over it… done
Chuck

Hank: 46 Chev 1/2ton shortbed
2023 Miata RF Club