Hi Vanilla,
Welcome to the Mattress Forum! 
[quote]Would you recommend Spinal Care?
Would you recommend Diamond Manufacturer in general?[/quote]
There are some comments about Diamond in post #2 here and the posts it links to that would be well worth reading. I had a conversation with someone from Diamond a bit ago about some new mattresses they are designing and I passed on my thoughts that it would be very helpful if they were more transparent about the type and quality/density of the materials in their mattresses so I hope that they will take the comments to heart.
Spinal Care is a smaller independent manufacturer that makes some good quality/value mattresses that would generally be a better choice than many of the larger or major brands. A specific term site search on Spinal Care (you can just click the link) will also bring up more comments and feedback about them.
Of course you would need to know the information listed in this article about any mattress you are considering (regardless of the manufacturer) so that you can make sure there are no lower quality materials or weak links (or any materials that don’t meet your specific criteria) in any mattress you are considering.
There is no detailed information about the quality/quantity of foams used in the Spinal Care or Diamond mattresses you mentioned, so until you are able to contact them and find out that information I wouldn’t be able to make any meaningful comments upon those products for you.
Phoenix