Hi darrylb.
Right now I lean FloBed, I don't know how I feel about doing a DIY mattress (beyond what a FloBed would be), and we were hoping to finance the bed (building wife's credit up). The price we actually have some flexibility on, and right now appears to be in the 3-4k range based on FloBed and FoxMattress being in that range. But that's also why I hope to get more feedback or suggestion on next steps.
It appears you have been receiving some excellent guidance from Mattrebuild. I’d add just a few more cents to the tally.
I was thinking flobeds before, but it doesn't have an adequate topper for my wife (and no way to evaluate). FloBeds seems to think an Egg-Crate topper is great, but I have always found them the first thing to fall apart-degrade, so that one puzzles me as well.
As Mattrebuild mentions a latex topper of medium firmness will easily last a decade or so. The 2” convoluted latex at 28 ILD will act like a 16 ILD topper creating the soft but resilient cradle (takes on the shape of the body better which provides more even support and aids in better pressure relief), has a higher support factor you most likely need for your side sleeping. See FloBeds hardness specs in the image below. (This does not apply to you but FYI ...very soft ILDs (around 14) for higher BMI ranges under increased mechanical stress tend to wear out faster.)
From my discussions with them, they have settled on this design and use convoluted latex across their all-latex mattresses for decades because based on consumer feedback and reports of pressure point relief and better skin blood circulation (similar to the setup used for hospital patients post-operation)
Additionally, you can request to replace the convoluted layer with a solid layer of the same thickness latex and your choice of ILD (from 22 ILD to 36 ILD) if you prefer, or … you can initiate an exchange if you wish to try the convoluted version to experiment with.
Their vZoned mattress has 13 possible firmnesses (each side of the bed) and 100 Night Money Back Firmness Guaranteed Test Rest to get the right firmness. If returned during this time you’ll get a full refund, but you will have to pay for the shipping back. For example, a queen mattress would cost about $79 to ship to the Continental US. They offer their UPS account to return at the same price, so your risk would be about $148.
1. We understand our bodies are not straight, and that we need a lot more "give" in our hips and shoulders.
Again, it’s good to know FloBeds made it into your finalists. With its customization options, it has a high probability of being a good match for you and your wife as the vZone offers customized lumbar support, shoulder, and hip relief which will allow for your spine to settle in its neutral alignment. You can switch around the comfort layers until you are happy. I noted in the alignment photos you uploaded that the pillow elevation is too high and can add some pressure on your cervical (especially for your wife) I would address the pillow issue a little after the mattress purchase as the pillow/mattress combo is an important part of the alignment puzzle.
2. We really like talalay, but it needs a pretty dang good cover on top of it for my wife to like it. (Which is what Fox Mattress has)
FloBeds’ cover is organic cotton stretch knit quilted to organic wool which is preferred for its anti-bacterial and anti-fungal properties. The cover is good quality and also unzips for comfort exchanges, cleaning, and hanging in the sun and I don’t see any red flags that may be cause of concern. Is there something specific that your wife is looking for in a cover?
3. Fox Mattresses solution may not be quite "right" for us, but it sure as heck is getting closer.
This option has the advantage of store visits and maybe trying mattresses in several sittings. Many times, our perceptions change with our mood .. our bodies are funny that way... so it is a good idea to double-check that it is really getting closer to what you need.
4. We don't want memory foam
Yes, memory foam is not for everyone but many people got used to this particular feeling. Memory foam can be a "love it or hate it" material and it certainly has "weaknesses" that latex doesn't have even though they are roughly equivalent in terms of their ability to relieve pressure. You are probably wise to avoid it if your experience indicates you don't do well with it in the long term.
Just in case you want to peruse other options here are some other Trusted Members that offer Latex beds [some offering zoned options as well]:
Arizona Premium
Latex Mattress Factory
Nest Bedding
Foam Sweet Foam
My Green Mattress
Luma Sleep
It certainly looks like you are making great progress.

I'll be interested to learn of your eventual decisions.
Phoenix