Any micro SdCard will do but it's adviseable to go for 32GB of storeage space or higher. I believe you can go as high as 2TB. You're running the Marshmallow flavour of Android so you will need to nominate the card to be used either for Internal or Portable storage.
If Internal, you would be able to install some Apps on it but others will need to remain in the 16GB system storage. The option to nominate storage is on a one way basis - onbce you've chosen it, there are no half measures.
If all you want is Portable storage, make sure you back it up regularly. Phones can get lost and stolen so remove the card weekly, put it in a full size SdCard carrier and back up in your PC or laptop.