Hi jim1952,
The best “suggestion” I can give you would be to start with post #1 here which has the basic information, steps, and guidelines that you will need to make the best possible choices. In other words … my role is to help you with how to choose rather than what to choose.
I would normally suggest local testing on similar materials and designs even if you are considering an online choice so you are comfortable and familiar with the materials in a mattress you are thinking about.
Most of your questions though are really about personal preferences (such as the choice between memory foam and latex which are very much apples to oranges comparisons) and which like any preference issue can only be answered by the person themselves.
I’m happy to help connect you to good retailers and manufacturers and speak to the quality and value of a mattress or help you identify any potential “weak links” (and like all the members here … Brooklyn Bedding is among the best quality and value in the country) but your own local testing and/or more detailed conversations with each retailer or manufacturer you are considering is the only way to decide on which of the mattresses they offer is best for you in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences) and which one is the best match for what I call your personal value equation.
I also agree with you that an online mattress purchase that has options available for comfort changes after a purchase is much less risky and is part of its value although I would still make sure you are familiar with the general feel and performance of the materials that it uses.
Quality is something else completely because you can’t “feel” the quality of a mattress and it primarily determines how long a mattress will stay close to its original properties with less softening and breakdown of materials. This is why it’s important to know what is inside any mattress you are considering so you know the quality of the materials (of any type) are appropriate for your budget and can make meaningful quality and value comparisons with other mattresses.
I’m assuming you are in the Boston are if you are looking at Boston Bed Company so the list of better options I’m aware of in the Boston area (and they are one of them) are in post #2 here and post #2 here has some links to posts that have some feedback about some of them aw well.
So I would always start with local testing of materials and different mattresses so you are clear on your preferences regardless of whether you end up buying locally or online.
Phoenix