Hi embnels,
Welcome to the Mattress Forum! 
The My Green Mattress 7" Simple Sleep Mattress is a 6" 100% NR Dunlop latex core that rates quite firm (their rating of 32-36 ILD, or 8.5/10 on their firmness scale). The cover uses GOTS certified cotton and natural wool. This is a bit of more simple mattress and many adults find that they prefer a topper when sleeping on this mattress. It is not a customizable product. There is a 100-night exchange/return plan at a cost of $99.00.
The Spindle 10" Natural Latex Mattress uses three 3" layers of 100% NR Dunlop latex. The cover uses GOTS certified cotton and Eco-Wool certified wool. The product is customizable within 365 days after the purchase for a $150.00 layer change fee. There are comfort combinations from firm to plush offered.
Both Spindle and My Green Mattress are members here of the 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. I certainly wouldn’t hesitate to purchase a mattress from them.
When making an online purchase, your best course of action is to first have a detailed phone conversation with any manufacturer you’re considering and let them guide you through their selection process, and you can also become familiar at that time with their return/exchange policies. Their detailed knowledge of their mattresses and how they fit with different body types and sleeping positions along with your feedback from local testing can help lower the risk of an online purchase. Post #2 here and this topic have more about the pros and cons of a local vs an online purchase.
Regarding someone else’s satisfaction with a mattress, 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).
Vivetique has different all-latex models and the last time I checked all they use is Dunlop latex, but unless you are matching the exact same Dunlop with the same blend, the same density and ILD, in the same thicknesses and the same arrangement, along with the same cover, there will be a difference in feel. Additionally, the continuous pour process Dunlop used by Spindle has a different feel from traditional Dunlop that is cured and poured in molds. You can use your local testing as a reference when phoning a manufacturer and they can assist in finding a model in their lineup that might best approximate what you liked that you had tested personally. You’d want to find out the information about any mattress you tested in person first, of course.
You’ll always want to make sure that you find out the information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure 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.
From the simplest version of the Mattress Shopping Tutorial, choosing the “best possible” mattress for any particular person really comes down to FIRST finding a few knowledgeable and transparent retailers and/or manufacturers that sell the types of mattresses (see this article ) that you are most interested in (either locally or online) and that can provide you with all the information you need to know to make an informed choice and make meaningful comparisons between mattresses and then …
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Careful testing (hopefully using the testing guidelines in this tutorial) to make sure that a mattress is a good match for you in terms of “comfort”, firmness, and PPP … and/or that you are comfortable with the options you have available to return, exchange, or “fine tune” the mattress and any costs involved if you can’t test a mattress in person or aren’t confident that your mattress is a suitable choice.
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Checking to make sure that there are no lower quality materials or weak links in a mattress you are considering relative to your weight/BMI range that could compromise the durability and useful life of the mattress.
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Comparing your finalists for “value” based on #1 and #2 and all the other parts of your personal value equation that are most important to you.
I’m interested to learn how you progress with your decision-making process.
Phoenix