The mattress already came thinner in the middle and thicker in the head and feet of the mattress.
I kept it, because I thought it will come to  the right position by itself as usually mattresses do.
Unfortunately since 15 July 2020 it went only worse.
This mattress has been bought for 11 years old child, so not a heavy person was sleeping on it. My child started to have a serious problems with her spine because of this mattress.
I need to change this mattress immediately for her (that's what doctor said). This mattresses supposed to be orthopaedic and it wasn't cheap.
I am very disappointed, because the brand of this mattress is a top brand on the market. Unfortunately it doesn't meet even basic standards.
I will not recommend it to no one, especially not for children, who supposed to have best sleeping place as they are still growing and it's very easy to damage their spine like it happen to my daughter.