here it is 500 maybe

get the hardest you can find

it will be the healthiest

people slept on the floor for many 1000 years

in japan people use futons, thin and hard

your body will adjust

if you choose a soft mattress your body will develop unnatural positions and you will feel back and or joint pain after some time, if you are young it can take years before you feel it.

in the usa and in europe it is a multi billion dollar industry to sell you what you do not need and what is not even healthy for you for thousands of bucks