If you are trying to go with the simplest solution for the users of your home and are not trying to automate the lighting in that area with motion sensors or other intelligence then your best bet is to replace those switches with GE versions such you can purchase from SmartThings directly, Amazon, or Lowes. You do need to know or learn how to replace a switch however.
I would like intelligence. I need to be able to control each light with my smart phone in be able to create schemes involving motion sensors particularly at night time. In looking at the products on the smart things I’m a little confused on whether or not I need two smart switches or just one smart switch and an add on to replace my double rocker paddle switches?
You could add a dual relay unit to the existing switches to add Z-Wave control. In that case, your switches stay in place and become toggles that can also be controlled by SmartThings.