HI Random84,
Welcome to the Mattress Forum! 
Thank you. The goal of this site is to promote transparency and the ability for consumers to educate themselves and find out the information they need to know to make an intelligent purchase. Any bias I have is to products and manufactures offering such products or guidance. 
You’re skipping a few steps here (which may be why you are “scratching your head”), and you’d want to go back and review the complete mattress shopping tutorial. Much of this focuses on consumers first educating themselves regarding better quality componentry and attempting to find products/components that may suit their needs. And if specific products are found that might have a potential for suitability, and if these products are online, then the most reliable source of guidance would 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 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, options, and firmness levels to different body types, sleeping positions, and preferences (or to other mattresses that they are familiar with) than anyone else. Their detailed knowledge of their mattresses and how they fit with different body types and sleeping positions along with your feedback from local testing, a customer base of many people that they can use as reference points, and any exchange, return, or any options they have available to customize a mattress after a purchase can help lower the risk of an online purchase. These online retailers or manufacturers can also be a good “value reference” for local purchases to make sure that if you are paying a “premium” for a local purchase (in exchange for the kind of “in person” guidance, service, and value that comes with dealing with a local retailer that can help you make more “accurate” choices that you have tested in person) is not too high.
As I wasn’t part of them, I can’t speak to your personal “chat” sessions, but your experiences are much different from the ones I have, as well as ones relayed by many members here on the site. Some representatives are more knowledgeable than others, and some companies are more transparent than others. And of course there’s the difference in how adept different members are at asking questions that are the most germane to knowing if a mattress contains quality materials. For example, ILD is considered more of a “comfort spec” and many manufacturers consider this information proprietary for polyfoams, with the more important information being the density of the polyfoam in question. All the information you need to know when asking about a mattress is in this article. This is also one of the reasons I suggest a detailed phone call versus a chat session or email, as you’ll be able to receive more accurate, voluminous and real-time information about any product. It’s also more difficult for representatives to infer intent via a chat feature, as mattress companies are well aware that many people are simply attempting to replicate what they offer by finding out overly-detailed information of their products and then attempting to create it themselves via purchasing their own materials.
As for finding information about a product on their web site, different companies may disclose densities on the pages for their specific products, some may place them on their FAQ pages, and you may have to phone to gather more detailed information – every company chooses what information they wish to share and how to do so. Some company’s web sites are more elegant and complete than others. I’ll be the first to admit that not all mattress manufactures have the most up-to-date web sites. And regarding Christeli, you wouldn’t be able to find that their base foam is 5 lb – because it isn’t. That is not a density used for polyfoam support cores. You may wish to do more reading about foam densities for different materials here. They use a 2 lb density polyfoam core, which would be a good quality and durable material. And the specifications of their line is also listed conveniently for you here as well.
While I can certainly help with “how” to choose, it’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP (Posture and alignment, Pressure relief, and your own Personal preferences) or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
Based upon some of your assumptions about foam densities that are incorrect and your “admitted limited” research, the first thing I would suggest you do is read through the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase 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 all the 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).
Outside of PPP (which is the most important part of “value”), the next 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 see or “feel” and assessing the durability and useful life of a mattress depends on knowing the specifics of its construction and 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 find out the information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure 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.
Also if you are of a higher BMI, it presents special challenges and generally requires firmer materials (in the support layers especially). This could be firmer latex or innersprings (the type of support component would be a personal preference and in the right design either could be suitable) or even a zoned construction. The same overall guidelines apply with higher weights though that PPP (Posture and alignment, Pressure relief, and Personal preferences) along with using high quality durable materials that will maintain their feel and performance for longer periods of time are the way to make the best choices. Heavier people in general will need firmer and thicker comfort layers and firmer support layers than those who are lighter and because no materials will last as long with much higher weights the quality and durability of the materials and components is even more important than normal. I wouldn’t “rule out” any types of mattress and base your choices on your own personal testing. Post #3 here has more information and suggestions about higher BMIs that is worth reading.
You seem to be having a consistent poor experience with whatever mattress company you chat or phone (which isn’t consistent with what most site members here experience), so my hope is that the information I’ve linked to in this post will assist you with your research and result in more positive future interactions with any company or manufacturer you contact! :cheer:
Phoenix