I think the interlocking foamy tiles parents should put on kids' floors are just the right consistency. You will offend neither the isolation camp nor the coupling camp.
The tiles are usually in bright colors but also are sold in dark grey. The typical size is 24"x24" and I bought a package of 4 for $9. Just cut with a box knife or big scissors. Cut towards your chum not your thumb.
I think the tiles with the coated "diamond plate" shapes on top might be a bit more durable than just flat foam but who knows.
These tiles are also popular at some piano schools. Put a few on the bench to instantly change the height. They are dense enough but also comfortable. My dad stole a few to cushion his computer chair.
You can find the tiles at Walmart, Lowes, Home Depot, ACE Hardware, maybe some of the big home junk-decoration stores. Here are some examples:
I find the foam durable and robust; effectively kid-proof. Regardless, I would keep the felt between the foam and the furniture to help protect against scratches and any paint reaction of the foam which will deteriorate after years.