Need quick advice on which of these 2 mattresses be better for side sleepers.
Ultimate Dreams Natural Latex Matress vs Ultimate Dreams 13" Gel Memory Foam Mattress
The choice between latex and memory foam is a preference and one is not “better”’ than another for side sleeping or any other body type or sleeping position. It depends as much on body type, the design and firmness of the materials, and your own preferences as it does the material. You can read a little more about the differences between them in post #2 here.
The Ultimate Dreams natural latex mattress is actually a choice of several mattresses depending on your choice of comfort level so it would also depend on the comfort choice you were comparing. In general though the 13" gel memory foam would probably be softer for most people if that is a consideration.
Some side sleepers would strongly prefer softer latex while others would just as strongly prefer memory foam. There really is no “better or worse”. Which is better … an apple or an orange?
Post #2 here has more about making comfort choices and as you can see the best way to choose would be your own personal testing on similar mattresses or if that isn’t possible a more detailed discussion with the manufacturer who knows more about their mattresses and which options will best match different people “on average” than anyone else.
I would strongly encourage you to only purchase a mattress that uses a material you are familiar with because the difference between memory foam and Dunlop latex is night and day even though both are good quality materials.