Hi just1chancefree,
As you can see in the guidelines here … I would avoid Sealy or any manufacturer where you aren’t able to find out the quality of what is inside it (and Sealy doesn’t provide this).
You can see the guidelines I use for memory foam mattresses in post #10 here. If they are made offshore and they have CertiPur certification then they would meet the guidelines (as long as they are around 4 lbs or higher density). There are some good foams that come from China and a lot of cheap junk
3" of 3 lb memory foam would be a “weak link” I wouldn’t consider.
Phoenix