What is the best birth control method for teens?

I accidentally put this in the "Avoiding Pregnancy" tab, oops! 
I'm sexually active and never fail to use a condom when being intimate with my long-time boyfriend. But, I would like to have an extra "barrier" to use in conjunction with condoms for added protection. I know most teens use BC pills, but I would like something that lasts longer & is more effective, like an IUD or the Implanon/Nexplanon. What method do you ladies think would be best for me, that is also affordable for a working teen? (I don't plan on using my parents' health insurance, because I would like this to be confidential.) Thank you so much in advance!