Hi spunkyk014,
Firmness and softness is very subjective and what feels too firm for one person can feel too soft for the next depending on individual body type, sleeping position, and personal perceptions and preferences. There is no firmness rating that applies to all people and different manufacturers also have different descriptions of the firmness of their mattresses that are not directly comparable. There are also different types of firmness and softness (see post #15 here).
Based on your description … it sounds to me like you may do well with a topper to add some extra pressure relief to your mattress. Post #2 here also has some suggestions that may be helpful before you consider a topper but if you do decide to add a topper then post #2 here will also be helpful although your budget will limit the quality of material that is available. If you do buy a low cost topper that works well for you then at least you would be able to replace it without replacing the whole mattress.
Phoenix