Hi BeachGirl,
Most consumers wouldn’t be able to tell the difference and would be dependent on the integrity and knowledge of the retailer or manufacturer they were buying from and the accuracy of their descriptions of the materials they were using. Besides any differences in natural latex content there are also two different types of latex manufacturing methods which are also different in their performance and “feel”. You can read a little more about the different types of latex in this article and post #6 here. The choice between them would be based on personal preferences and priorities and I would think of the different types of latex as being “different” and more or less suitable for you in terms of your specific needs and preferences and your personal value equation rather than being “better or worse” in and of themselves. Better in one person’s “definition” or context may be worse for another person depending on what is most important to each person.
I think very highly of both Flexus and Foam Sweet Foam and both would make good quality/value choices.
My opinion of Astrabeds is not nearly as high and their “value” is also not in the same range as either of the other two (or other online choices that are available as well). You can read more of my thoughts about them in post #2 here.
You can read more about different types of mattress / foundation combinations in post #2 here but in most cases a latex or any all foam mattress will do best on a rigid slatted foundation that has firm non flexing and even support and gaps between the slats of 3" or less. There are some thinner latex mattresses that have been specifically designed as a “sleeping system” for use on a specific box spring however and in these cases they should be used with the box spring they were designed for.
Each manufacturer has their own warranty criteria so it’s always a good idea to check with the specific manufacturer of your mattress but in general … unless a latex mattress is specifically designed to be used on a specific box spring … then I would use a rigid non flexing foundation.
Phoenix