Hi chadyoung,
Welcome to the Mattress Forum! 
The very first thing I would suggest is that you consider “resetting” how you are going about making a final selection for your mattress.
Making recommendations is the antithesis of what this site is about, and instead I focus more on the “how” to choose and not the “what” to choose. While other people’s comments about the knowledge and service of a particular business can certainly be very helpful … I would always keep in mind that you are the only one that can feel what you feel on a mattress and I would be cautious about using anyone else’s suggestions, experiences or reviews on a specific mattress (either positive or negative) or review sites in general as a reliable source of information or guidance about how you will feel on the same mattress or how suitable or how durable a mattress may be for you. In many if not most cases they can be more misleading than helpful because a mattress that would be a perfect choice for one person or even a larger group of people in terms of comfort, firmness, and PPP may be completely unsuitable for someone else to sleep on (even if they are in a similar weight range). In other words … reviews or other people’s experiences in general won’t tell you much if anything about the suitability, quality, durability, or “value” of a mattress for any particular person (see post #13 here).
Another one of the risks of using this type of information as a basis for choosing a mattress is that people are also very different and if you choose a mattress based on the premise that “many people seem to like this type of mattress so I will probably like it as well” it can create unrealistic expectations because any individual (and for that matter most individuals) may be very different from the “average” of a group in terms of their body type, sleeping positions, and preferences and there is no way to know whether the specific mattress they are considering was even included in the group or has any weight in the results.
With that being said, I can offer some comments based upon your selection criteria.
The Plush Beds Botanical Bliss 9" mattress you mentioned is all latex (6" GOLS Dunlop core with 2" Natural Talalay on top). The cotton ticking is GOTS certified and the wool is Eco Wool. The layers are not glued together, and the Talalay layer is exchangeable. You can see some of my comments about Plushbeds in post #2 here. They use some good quality and durable materials, but they also do a lot of internet advertising, so I’d be cautious of some of their “discount claims” when entering into your value equation.
The SleepEZ Organic Select Sleep 10" mattress you mentioned uses three 3" layers of latex (GOTS certified Dunlop or Natural Talalay), so it’s a bit more customizable. The cover uses GOTS certified cotton and GOTS certified wool. Their layers are not glued together, so you can rearrange/exchange layers.
The Spindle 10" Natural Latex Mattress uses three 3" layers of continuous-pour natural Oeko-Tex certified Dunlop latex. The cover uses organic cotton and the wool used is Eco Wool. The layers are not glued together and are configurable like the SleepEZ with three layers.
The Sleep on Latex Pure Green Natural latex mattress is not a configurable product, so it falls outside of one of your preferences. You would choose either a soft, medium or firm configuration. The 9" uses a 6" Oeko-Tex certified natural Dunlop latex core with a 2" natural Dunlop latex piece glued on top of that. The cover uses GOTS certified organic cotton yarn and wool.
Return/exchange fees of course have a cost, and most companies choose to build them into the cost of every mattress they sell. Spindle chooses to charge a fee for returns/exchanges only to those who ultimately choose to take advantage of those policies as a way to keep the overall price down on their products, and they do offer a longer exchange period (365 days) to accommodate that. Not everyone likes exchange plans that are set up in that manner, so that would be part of your own personal value equation.
Talalay latex has a different feel and is more expensive to produce than Dunlop latex. The “value” would be entirely up to you in the comfort that the Talalay provided versus Dunlop latex. Choosing Talalay or Dunlop isn’t a better/worse choice, but more a personal comfort preference choice.
There is more about the 3 most important parts of the “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 of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
The SleepEZ foundation would be the heaviest-duty foundation of the ones you’re considering. You certainly could build you own and there are many online plans available, as well as coverlets.
The good news is that overall you are certainly looking at some mattresses using good quality componentry.
SleepEZ, Spindle and Sleep on Latex are all members of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations, and I would not hesitate to recommend them for your consideration.
Good luck in your selection, and let us know what you decide to do.
Phoenix