Hi Ez1,
I can only comment on the quality or value of the materials and mattresses and any potential weak links they may have because there are too many variables and unknowns (body types, sleeping styles, preferences, physiology, age, health conditions, sensitivities to different factors etc) to use any formula or “theory at a distance” to choose the best balance between comfort and support for any specific person (outside of the more extensive but generic information in the mattresses section of the site) … especially without a specific frame of reference that includes detailed descriptions of mattresses you have tried and the specifics of their construction. Only your own personal testing and/or more detailed conversations with each manufacturer or retailer you are dealing with can help you make good comfort/support choices. The most accurate way is always your own personal testing and the next best way would be longer conversations with each manufacturer or retailer who is much more familiar with the more detailed specifics of their own mattresses than anyone else and the types of people that “on average” will do best with each or their models or options than I am.
The foam materials are good quality (blended talalay) and comparable in all of them but you have more options and choices of the type of latex and the design of your mattress with SleepEz and BB. The cover on the Ecosleep is also different and less costly because the other two contain wool quilting and the Cassidy is an less expensive unquilted bamboo cover. The other differences are mostly about your ability to customize the layers both before and after a purchase so that you are able to “match” your ideal in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences) and about what your options are and the costs involved if your choices aren’t as close to your ideal as you hoped (which is an important part of any online purchase IMO.)
No matter what the cost or “commodity value” of a mattress … if it doesn’t match your specific needs and preferences in terms of its design then it would have little value to you. Either local personal testing on different mattress materials and designs or longer conversations with manufacturers and retailers that have the knowledge and experience to help you make good choices based on the “averages” of their customers that may be somewhat similar to you are an important part of the confidence you will have about the suitability of a mattress and IMO are important parts of the “value” of any mattress purchase and your own personal value equation.
You are looking at “all good options” though which is the most important part of making any purchase … no matter how difficult it may be to make final choices that are best for your specific criteria and preferences and give you the most confidence that you are making the best choice for you.
In my own case … it took me weeks to make a final choice as I weighted and measured all the pros and cons of each design down to the level of detail that in hindsight probably wasn’t all that meaningful in “real life” experience 
Phoenix