Hi kayche,
Thanks for the update and feedback … I appreciate it 
I’m not sure which mattress you have but most of the mattresses sold today come with a foundation that has little to no flex (similar to a platform bed) rather than an actual box spring with springs that compress. Actual box springs are very uncommon outside of some of the smaller manufacturers that still make them for their specific mattresses that do better with a box spring than with a foundation. In most cases … the cause of the “lumpiness” that you are feeling would be lower quality foams in your comfort layers or in some cases a mattress that doesn’t use a good quality insulator pad over innersprings that need them to prevent the padding over the springs from sinking into the springs.
The tutorial post includes a link to several lists of the better online options I’m aware of and there are many good options available to you.
There are too many unknowns, variables, and personal preferences involved and firmness is too subjective and relative to different body types, sleeping positions, and individual sensitivity for anyone to to be able to suggest any specific mattress that will feel firm to you or will be a good match for you in terms of PPP based on specs (either yours or a mattress) or "theory at a distance (see mattress firmness/comfort levels in post #2 here).
When you can’t test a mattress in person to assess how firm it feels for you then the best source of guidance will always be a more detailed conversation with a knowledgeable and experienced online retailer or manufacturer who will know more about their own mattresses and the firmness options they have available than anyone else (especially if they haven’t slept on the mattress in person).
Post #4 here along with posts #3 and #4 here include some of the better lower budget online options I’m aware of if you are in a lower budget range.
Phoenix