Hi Awatts,
I think brass has done a great job outlining the pros and cons of the options you are looking at.
Along the same lines … there is more about the most important parts of the “value” of a mattress purchase in post #13 here but the first priority is always how well a mattress matches your specific needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) and which type of material you prefer.
The Tuft & Needle is an “all or nothing” purchase that will either work for you or it won’t because it only has a single firmness option. If it works well then you would be set and if it doesn’t then you have the chance to return it at no cost to you.
The Spindle has individual component layers that can be rearranged in different ways (or a layer can be exchanged) so in effect it is several mattresses in one and you can use your sleeping experience to find the combination of layers that works best for you. Latex is a very high quality material and is the most durable of all the foam materials.
As brass also mentioned I would also try to do some local testing on latex (particularly Dunlop) so you can get a better sense of how you like the feel of latex in general. Polyfoam is the same material that is used in most sofas so most people would be familiar with how it feels at least in general terms. It’s also the material that is used in the comfort layers of many innerspring mattresses although it comes in many firmness levels. The 1.8 - 2 lb polyfoam that T&N uses is also a good quality material but isn’t as durable as latex.
Just to add one further possibility … the Dreamfoam 12 in 1 customizable here may also be worth considering as well. It uses 2 lb polyfoam and also has 3 component layers and has a cover with a different quilting pattern on each side of the cover so it can be customized in 12 different ways. It is similar to the Spindle in the sense that you can put the layers together in different ways to customize the firmness of your mattress but similar to the Tuft & Needle in that it uses polyfoam instead of latex.
You are looking at some very good final choices but as brass also mentioned they are also very different from each other and your preferences will play a major role in your choice.
Phoenix