Hi aminah,
The majority of people that are in your weight ranges would be fine with 8" - 9" of latex (depending on the type of latex, the design of the mattress, and their body types, sleeping style, and preferences) but of course personal preferences and the results of your own local testing on latex mattresses can also play a role here. You can read about some of the advantages of a thicker latex mattress in post #14 here which along with your own personal experiences in testing latex will give you a better sense of whether it would be worthwhile for you.
Phoenix