Hi jege41,
From a quality/value point of view it’s certainly good.
From a comfort performance point of view your own experience will answer the question more than any theory because I can never know what someone else may consider too soft or too firm.
The guidelines I use for a topper are in post #8 here and as you can see it’s a little on the thick side but this is also offset by the fact that it’s a medium rather than soft topper and that your mattress is also quite firm as well (and would probably make a good transition layer under the topper) so overall it seems like a good choice to me and because of Costco’s return policy especially … it certainly seems worth trying IMO.
Phoenix