Hi BojackHorseman,
Welcome to the Mattress Forum! 
[quote]I’m a bit on the heavier side, fluctuating around 220 (give or take five pounds), and I do worry about the longevity of the bed. Tuft and Needle worries me the most in this regard, as they’re newer to the scene. I also want something that will hold up to the stresses of an active couple, so to speak.
Flexus is all latex and has the highest prices, Nest is a good compromise on price but only on their non-Latex beds (Flexus is cheaper for all-Latex), and Tuft and Needle is by far the cheapest, but also uses polyfoam. Will polyfoam be able to stand up to heavier use? Is the price difference (about $1000) justified for a Flexus latex bed over a Nest non-latex bed, like the Alexander or Love Bed?[/quote]
There is more about the 3 most important parts of “value” of a mattress purchase in post #13 here 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 suitability, durability, and all the other parts of your personal value equation that are most important to you (including the price or course and the options you have available after a purchase).
While I can’t speak to how a mattress will feel for someone else … outside of “comfort” and PPP (Posture and alignment, Pressure relief, and your Personal preferences) the 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 “feel” and assessing the durability and useful life of a mattress always depends on knowing 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 or how long a manufacturer has been in business) so I would always make sure that you can find out the information listed here so you can compare the materials and components to the quality/durability guidelines here to confirm that 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.
There is more about Tuft & Needle and some of the other “simplified choice” mattresses in post #2 here in the simplified choice topic and as you can see there are no lower quality materials or weak links in their mattress relative to your weight range that would compromise the durability or useful life of their mattress.
The same would be true for the Nest Bedding mattresses and the Flexus mattresses of course and with higher quality/density and more durable materials there will also be more “bonus time” relative to the useful life of the mattress.
There is also more detailed information about the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here
That would depend on what your wife was allergic to (and avoiding those specific allergens). There is no specific definition or meaning for “hypoallergenic” (see here) and when it comes to mattresses this is more of a marketing term than anything else but the most common allergies are to dust mites particles and other airborne small particles rather than the materials in a mattress. There is more information about dust mites and allergies and methods that can be used to control dust mite populations or other allergens in post #2 here and in post #3 here. There is also more about allergy encasements in post #2 here.
There is more information about the different support systems (bedframes and foundations or platform beds) that are generally suitable for different types of mattresses and some examples of each of them in post #1 here
With an all latex mattress then it would be a good idea to use a slatted foundation or platform bed that has gaps between the slats of 3" or less. With mattresses that use a polyfoam base layer then slats with gaps that are about 5" or less would be “OK” although I would tend to use 4" as a more suitable guideline. Flexus suggests and sells a foundation for use with their latex mattresses … not a box spring (see the bottom of the page here).
ADMIN NOTE:Removed 404 page link | Archived Footprint: Latex Mattresses, Organic Latex Mattress, Pocket Coil Mattress - Flexus Comfort
Once you have narrowed down your options to a list of finalists that are all choices between “good and good” and none of them have any lower quality materials or “weak links” in their design relative to your weight range and if there are no clear winners between them (which is usually a good indication that you have done some very good research) then you are in the fortunate position that any of them would likely be a suitable choice and post #2 here can help you make a final choice based on your local testing or mattresses you have slept well on, your more detailed conversations about each of them, your confidence about PPP and the suitability of each one, their prices, your preferences for different types of materials, the options you have after a purchase to fine tune the mattress or exchange or return the mattress or individual layers, any additional extras that are part of each purchase, and on “informed best judgement” based on all the other objective, subjective, and intangible parts of your personal value equation that are most important to you.
Phoenix