Hi amanda3 
 
Thanks for your question, 
 
At heights and body weights you have provided, along with both of your sleeping habits, a medium spring tension mattress is what you require. From there your personal preference will influence the final decision. Each mattress has a unique comfort level. This is dependent on your sleeping habits. As you are both back and side sleepers you do not want to go for anything too firm in the comfort layer. 
 
I would advise having a look at either the Artisan Naturals or the Origins Pocket 1500. 
 

 
These are both a true medium in the comfort layers, with the Artisan range being made from predominantly natural fibres, and the Origins range being made from synthetic. This is reflected in the guarantee as the Artisan Naturals carries a ten year guarantee, in comparison to the Origins Pocket 1500's 3 year guarantee.