Hi picklex61,
The best firmness and thickness choice for a topper topper depends on the mattress it’s going on. It would also be helpful to know more details about what he was using before as a reference point for what he considers to be too soft.
Other than that … post #2 here and the posts it links to has some guidelines for choosing a topper that may be helpful.
For those that like the “feel” of latex it is certainly a very high quality and durable choice.
Phoenix