Carpet does not imo keep your feet warmer and at the same time is a pain in the ass when it gets snow, ice, leaves etc. Causes more problems than it helps.I use the closed cell foam ones as well. I am usually alternating every 30-45 minutes between sitting and standing.
I did add carpet to my stands this year. Hoping it keeps my feet warmer this late season!
To the OP....get a thick closed foam seat cushion. If you really want comfort buy a couple Millenium stands.