How to manage your hair

At this day and age, I have naturally wavy, thick, coarse hair that doesn't like to move. It just stays in the same spot all day and it's really annoying because if I want to grow it out, it just puffs out unless I comb it down. I want to get my hair straightened, but not sure if it will work the same as a relaxer. My mom went to school for this stuff and says hair straightening works the same as relaxing, but I don't believe that. Can anyone give me some pointers on this? Thanks in advance.