Hi dian,
You can see some comments about down alternative fiberbeds in post #6 here and the posts it links to. It can certainly provide some additional surface softness and a softer “feel” to your mattress but it can also reduce the ability of softer foam layers to contour to the shape of the body and won’t be as pressure relieving overall as a softer foam topper.
I’m not sure if they are available on Walmart but they are on Amazon at slightly lower prices.
Phoenix.