Being on top.

My boyfriend and I have been dating for almost 5 months and every time I have sex with him, it gets better. Like most guys, if we are doing it for a while, he gets tired and suggests I get on top. I love to make him happy, so I do it. However, I do not like being in charge and controlling things, so this is not the best position for me. How can I be on top and enjoy it, while also making sure he's having a good time too?