Hi Jjsshealy,
Just in case you haven’t read it yet … I would make sure you’ve read the tutorial post here which has all the basic information, steps, and guidelines that you will need to make the best possible choices.
Christeli is one of the manufacturers that are listed in the memory foam list that is linked in the tutorial post (see here) and I would consider them to be among the better online choices.
A forum search on Christeli Charleston will bring up more information about it but it certainly uses good quality materials (8 lb and 5.3 lb memory foam in the comfort layers and 2.0 lb polyfoam in the support core) and there are no weak links in the mattress. It is designed to approximate the Tempurpedic Allura so if you have done some careful and objective testing on the Allura and it’s the best match for you out of the Tempurpedic lineup in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) then the Charleston would certainly be worth considering. (NOTE ADDED: they are now using 6 lb memory foam in their mattresses)
Memory foam and latex are very different materials that have very different properties but the choice between them really depends on which one you prefer. There is more about the many differences between them in post #2 here and the posts it links to but the best way to know which one you tend to prefer would be based on testing each of them in person at local retailers.
Phoenix