Hi cat,
Welcome back … it’s been a while :).
Unfortunately, there are so many unknowns, variables, and personal preferences involved in choosing a mattress that personal testing is the part of choosing a mattress that nobody can do for someone else. His own testing will be much more effective that anything I could suggest based on “theory at a distance” because nobody else can feel what he feels (see mattress firmness/comfort levels in post #2 here).
It would be useful though to know the specifics of the mattress that he thought was “perfect” so he could use it as a reference point because without knowing this … unless you were to purchase that exact mattress … the time you spend testing a mattress where you can’t find out what is inside it is mostly wasted (see this article).
I would make sure you’ve read post #15 here and the links in option 3 before designing and building your own DIY mattress out of separate components when you haven’t tested a specific combination in person that you can use as a blueprint. It’s generally less risky to go with a “standard” component mattress that has a proven design and is close to what you have tested in person or where you have good options available after a purchase if you need to change any of the layers in your original choice. If you do decide to go in the direction of a complete DIY mattress that you design yourself then it’s important to make sure that you have realistic expectations of success and any costs involved if you make a choice that is less than ideal and need to replace any of the layers from your original choices.
The “best” approach to a DIY design (outside of a specific component mattress) is a “spirit of adventure” and a willingness to experiment through trial and error and where what you learn and the process itself is just as important as any cost savings you may realize (which may or may not happen).
Just to make sure you’ve seen it as well (because there may be some additional options since you were last here) … post #21 here includes the members of the site that sell online and many of them sell component latex mattresses with a wide range of designs, features (including side to side splits for couples with different needs and preferences), exchange or return options, and prices.
Phoenix