Hi dlireland,
I believe that a mattress is one of the most important purchases you can make and I don't know of any other furniture purchase that can have as big an effect on your overall well being over the next decade or so. Because of this I think it's important to do some initial research and some local testing to find the best possible quality and value that will fit your needs and preferences (for both of you). No matter how fatigued he may be with shopping ... that's not nearly as fatiguing as sleeping on a mattress that doesn't match your needs and preferences for many years ... or having to start all over again far too soon because your choice doesn't turn out to be suitable or lacks durability.
There is a
step by step set of guidelines here
about how to find the best possible mattress for you (which I'm guessing you've already read) but it seems to me that you have an even more important step that needs to come before these which is agreeing between you what needs to be done next and unfortunately I can't help you with that one

.
As I see it you have several options.
1. Buying the mattress that your husband wants and paying the price both in terms of the initial cost of your purchase (it's not very good value because of the materials in it) or in terms of how long it may last you and keep its comfort and support.
2. Both of you test mattresses together so that if you test other materials (such as latex) or look for a memory foam or gel memory foam mattress with better quality/value that you both know it's what you want. It doesn't seem like he wants to do any further testing though based on your comments.
3. Agree between you that you will choose the mattress. This to me is also risky because your husband may not like your choice (latex and memory foam are very different) and then you once again are in a quandry about what to do next.
I like the idea of the latex mattresses that have layers that can be changed, but my husband just wants someone to bring the mattress in, set it up and be done. How difficult is it to assemble a king size mattress that is shipped in layers? We would have to bring it to the second floor through a stairway with a low ceiling.
The components come in several boxes and while latex is heavy ... it is no problem for two people and it would go up stairs and around corners under low ceilings without any problem. The assembly process is also straight forward and any two people should have no problem with it.
Do you have any suggestions for me? I will likely check out Original Mattress Factory and the Healthy Back Store. I am hesitant to try The Organic Bedroom, because they bill themselves as a luxury outlet, and I fear falling in love with something I have no hope of being able to afford! But perhaps I can get some ideas? How should I approach this?
I would never buy a mattress on the same day as you are doing any testing so you can check to see if something similar is available to you with significantly better value either locally or online. All your local testing can be valuable whether you make a purchase there or not. The Organic Bedroom has some good latex options but they will also likely be significantly higher priced than similar options that are available online (or perhaps others that are available locally as well) so you can test mattresses there and then compare what they carry to other local and online options. Local is always "safer" than online and is well worth a "premium" IMO but if the premium is too high and they are significantly higher than other similar mattresses that are available online (I use a general guideline of about 20% but of course this is up to each person) then your local testing there can also help you make better choices.
Also, our bed is a platform bed from RoomandBoard with steel slats/beams. The slats are about 2.5" wide and 4" apart - would we need additional support? The bed is designed to not require a foundation for the mattresses Room and Board sells, but I don't know if it would be sufficient to satisfy a warranty for other mattresses.
IMO ... the gaps are a little bit too far apart for a latex core but should be fine for mattresses that have a non latex core. They would be OK for the short term but in the longer term its better to have something more supportive underneath to prevent the latex from compressing into the gaps.
Something like this
could make a good choice between the bed and the mattress to even out the support or you could add some extra slats if that was possible.
I stopped off at Original Mattress Factory on my way home and tried out their latex mattresses. The Latex Supreme was definitely too soft for our tastes. The Latex Foam mattress was better, but still seemed a little on the soft side to me. Their website indicates that their support core is 30-34 ILD, so I'm guessing that we will probably need something a bit higher with a comfort layer? I'm also not exactly a fan of the polyfoam quilting as this seems like a weak link.
They put their mattresses on an active box spring which will make them feel softer than they would on a firm slatted foundation. It may be worthwhile testing these on one of their adjustable beds or a firm surface that was rigid like your bed because it will likely change the feel.
The 1" quilting layer is not really thick enough to be a "weak link" because it is already very soft and further softening with a layer this thin wouldn't have any real effect. My general guideline for a quilting layer is that in the range of an inch is usually fine. Thicker than that (2" or more) is when softening can lead to alignment issues.
So hopefully you have the chance to do some further testing but most importantly decide between you what the "best" next step is so that both of you are on the same page and that he's OK with sleeping on a mattress that uses material that he's never tried (or perhaps agrees to try one or two latex mattresses) ... even if you end up doing most or all the legwork

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Phoenix