No, a mattress protector is not designed to affect the comfort or softness of your bed.
It only acts as a thin layer to safeguard your mattress.
Sometimes you'll be able to find quilted mattress protectors that offer a little more cushioning, but this is not enough to make a noticeable difference to the overall feel of your mattress.
If you’re looking to change the firmness of your mattress without having to replace your old mattress, you’ll need to look for a mattress topper.