Turning a mattress

Can you possibly tell me how you turn a kingsize mattress where there are 2 different firmnesses? We are looking to buy a new mattress and through your site we have discovered that we may need to different firmness ratings. I am 5'2" and 15st and my husband is 6'3" and is 14st.
We have an ottoman base with arched slats and are looking for the best mattress for us as we are sick of buying mattresses only for me to wake up each morning with chronic back pain or painful hips.
Thank you for your help.