If you have a sprung slatted base then it will feel different to when the mattress is placed on a platform top base, because this type of solid base give the mattress a firmer feel.
As a general rule of thumb the higher the spring count in our mattresses the firmer they are. However, we also include in our range of products Ortho mattresses. These are firmer still than other mattresses in our range.
You should try both the 2000 Classic and the 2000 Ortho to see which you prefer before making your purchase.