Hi izzi81,
I don’t think there is any “fault” in any of this … it’s just the type of choices that so many people make because there are so few sources of meaningful information in the industry … at least that are easy to find in all the “noise” of marketing claims and misleading information. As you mentioned at least you are in a position of being able to make more informed and “best possible” choices even if you are a little more limited in what you have available.
If you choose either a mattress that you know has good quality materials that works well by itself or choose a mattress that has the least possible low quality or unidentified foam (which will likely be too firm) and then add a good quality topper to customize your own comfort layer, then either way you have much higher odds of ending up with a better sleeping system than you would have chosen otherwise and that’s a lot better than the alternative where the same cycle could end up repeating.
If you do choose a “base mattress” that needs a topper (because there are no mattresses available that you can verify that the comfort layers are good quality) then sleeping on it (perhaps uncomfortably) for a short while can help you identify the type of topper that would work best with it using the information in post #2 here and the posts it links to as a guideline.
I think you will be fine not only now but even more so the next time you need a new mattress (or topper) as well
Phoenix