Trying to replicate Ikea Morgedal Firm Mattress Hardness

Hello- I have some questions about replicating the firmness and hardness of the now no longer sold Ikea Morgedal mattress. I need to purchase a new mattress and I read through this post as it had the same question (except for the medium-firm version).

I went ahead and purchased the Nest Quail Firm Mattress. The firmness of the mattress is good, however the top layer is softer than I would like. Something I really appreciated about the Ikea mattress was the hardness.

I am curious if anyone has suggestions on:

a) other mattresses that might be a better firm/hard combination to replicate. Note i’m open to anything (e.g. hybird etc)
b) ways to modify the nest mattress to make it more hard (e.g. topper)

As an additional note I recently tried the Helix Twilight Luxe with the Ergo Align layer and it felt more firm/hard than the Nest Quail.