Hi Olichar,
I can’t provide any specific suggestions because I can’t feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved in choosing a topper that will be a good match for you and your mattress based on either specs (yours or a mattress) or theory at a distance (see mattress firmness/comfort levels in post #2 here).
Having said that … post #2 here and the topper guidelines it links to can help you use your sleeping experience and your best judgement about “how much” additional softness and pressure relief you need as a guideline to help you choose the type, thickness, and firmness of a topper that will have the best chance of success and also includes some good sources for toppers that will likely be a lower cost, a wider range of firmness options, and have better exchange options (in case you make a mistake in your choice) than a PLB topper as well.
If you are in doubt I would probably tend towards a little thinner rather than a little thicker because it’s less risky in terms of exchanging a pressure relief issue for an alignment issue.
Phoenix