How about regular pt 5/4 x 6 board? Can be water coated to the color of choice? Right now I have the same size, plus awning covered so it extends more.
I have a good quality outdoor carpeting on the porch and the concrete steps leading up to it. Nice on barefeet and will not get hot. I replaced the carpeting after 8 years or so for about 500 us bucks.
Note, I do not have the 5.4 under it but have built nice porches and decks using it.
Regular grooved pine under carpet looks and feels fine to walk on.