A Possible Solution
The same thing happened to me we have very similar stories. I became too friendly with my straightener and my hair got damaged. It used to be halfway down my back like yours was when it was curly and now its just a little past my shoulders. Now, I dont even bother straightening my hair and I wear it natural slowly, but surely my curls are coming back. If you decide to wear it curly, make sure its well hydrated you might need to start doing deep conditioning to your hair to keep it bearable and soft. Good luck getting your curls back. Remember, It takes time so be patient and you should soon see results.