As mentioned by mesozoic, that's not great for side sleeping, which I do probably 75% of the time. My current mattress also provides me more lumbar support in back sleeping vs sleeping on a hard surface which I've done before. It's simultaneously firmer but more filling than a standard mattress if that makes sense. Additionally for non-sleeping purposes the give is necessary.
Nothing beats plain wooden planks + 3-4 woolen blankets on top.
Made the move to sleeping on harder surfaces about 15 years ago and never looked back - now occasional sleepovers at hotels leave me tired.