Ortho is a term loosely used by manufacturers to refer to extra firm models in their range, so avoid mattress that use this description.
The Emeline, available with or without memory foam will feel less firm than the Hartwell Ortho. Comfort is very subjective. A mattress that is too firm leaves parts of the body unsupported, creating pressure points on the parts of the body that are in contact with the mattress. A soft mattress may feel very comfy initially, but a mattress that is too soft will allow the lower back to sink into it too far, throwing the spine out of alignment.