Hi Codacon,
You’re most likely correct that what you have is firmer Dunlop.
You’ve probably seen this but some of the better topper options I’m aware of are listed in post #4 here.
I should also mention that the 5% discount or “bonus” that the manufacturers here have agreed to provide to members of this site applies to mattresses only not any other products they may sell (although it never hurts to ask as long as it’s not an “expectation” :)).
Phoenix