Hi Another Heavy Sleeper,
There is more information about the 3 most important parts of “value” of a mattress purchase in post #13 here which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and all the other parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
While I can’t speak to how a mattress will feel for anyone else because there are too many unknowns, variables, and personal preferences involved that are unique to each person … outside of “comfort” and PPP (Posture and alignment, Pressure relief, and your Personal preferences) the most important part of the value of a mattress purchase is durability which is all about how long you will sleep well on a mattress. This is the part of your research that you can’t “feel” and assessing the durability and useful life of a mattress always depends on knowing the type and quality of the materials inside it regardless of the name of the manufacturer on the label (or how a mattress feels in a showroom or when it is relatively new) so I would always make sure that you can find out the information listed here so you can compare the materials and components to the quality/durability guidelines here to confirm that there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase.
The BestMattressEver uses latex comfort layers and a 2 lb density polyfoam support core which are all high quality and durable materials and there are no lower quality materials that would be a weak link in the mattress relative to your weight that would be any cause for concern and it would certainly make a great quality/value choice for any weight range in a suitable firmness level.
While your own careful testing or personal experience is the only way to know for certain whether any mattress or combination of layers and components is a good “match” for you in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and your Personal preferences) … when you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (fast or slow response, resilience, firmness etc) and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs and firmness levels to different body types, sleeping positions, and preferences (or to other mattresses that they are familiar with) than anyone else.
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Any mattress with a polyfoam support core will do best with a firm, flat, and evenly supportive support surface underneath it that has minimal to no flex under the mattress and for larger sizes with at least one center support beam that has good support to the floor to prevent any sagging in the middle of the mattress. The components need to be strong and durable enough to support the weight of the mattress and the people sleeping on it without some of the parts bending, sagging, shifting, or breaking with extended use. The support surface under the mattress should have enough surface area to prevent the mattress from sagging through any gaps or spaces in the support surface over time but still allow some airflow under the mattress. I would suggest that the gaps between any slats are no more than about 5" (with 1 x 3 slats) although less than 4" would be better yet.
There is more information about the different support systems (bedframes and foundations or platform beds) that are generally suitable for different types of mattresses and some examples of each of them in post #1 here and some of the information and comments in this topic may be helpful as well.
The Ikea support systems are flexible slat systems that can change the feel and response of the mattress and they wouldn’t be my first choice for your mattress.
Phoenix