Coconut oil is amazing, but be so careful when it comes to oil in hair because it can easily go overboard and leave you looking too greasy.

Find a ceramic hair straightener. It doesn't matter if it's "high quality" (see: expensive). If it's ceramic, it'll get the job done.

I just section my hair off into different parts and straighten it that way. Make sure your hair is totally and 100% dried before straightening! There are tons of youtube videos on how to straighten and maintain curly hair, I bet they could help.