If you just want to share a bed, Cpt. A., you can ask for a "cama matrimonial," and they will give you a full sized bed. The singles are very small, even for young and slender people.

Also, if you are willing to share a bathroom instead of a bed, you will be able to find many affordable hostals in most price ranges.

What is your price range, btw? If you search here you will find something in your price category.