https://www.amazon.com/gp/product/B00GTCL44O/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I bough the 8 inch mattress almost a decade ago now and it's still going strong and is probably the comfiest mattress I've ever slept on.

https://www.amazon.com/gp/product/B00GXUM0M2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

And I just use this for a "box spring replacement".