Hi Elcan,
In a king size … you are certainly in the range for a latex hybrid (latex comfort layers and polyfoam or an innerspring support core) but you would be at the bottom of the range for an all latex mattress and it would have less latex in it which may or may not be suitable for your specific needs and preferences. A latex hybrid would be similar to a memory foam mattress (all memory foam mattresses use memory foam in the comfort layers but not in the support layers because memory foam is not supportive enough to be used as a support layer) except the comfort layers would be latex instead of memory foam.
The choice between them would be based on your personal preferences rather than “better or worse” because they have a very different ‘feel’ and performance and each person may have a different preference. Regardless of which type of material you may be leaning towards though “in theory” … its important to test both of them locally if that is possible to see which you prefer in real life. They are very different. No matter which material you prefer … it would be important to make sure that you use the best quality of either that was available in your budget range (along with any other layers or components that were in the mattress besides just the memory foam or latex).
There are some good online options available from the members here for latex hybrids or even all latex mattresses that use less latex that are in your budget range listed in post #21 here.
Some of the better options and possibilities I’m aware of in the mobile area are listed in post #365 here and I would call each of these to see whether they have any all latex or latex hybrids on their floor that you could test. This will give you valuable reference points and guidelines about your preferences regardless of whether you buy locally or online.
Phoenix