I assume this is the same thing as a mattress topper. I very recently got one for my 8-yr old mattress and it feels like a new mattress. My bed always felt good before, but this brings it to a whole other level! The 2-inch one was good enough.
Linenspa Gel Infused Memory Foam Mattress Topper
https://www.amazon.com/dp/B01N41ILAB...ing=UTF8&psc=1