Tips on spicing things up

I just wanted to get some advice or some good ideas on how to spice things up in the bedroom with my bf. He loves missionary and while I don’t mind it, i just don’t want to fall into the same routine. We also do me on top position but it’s pretty much those two.... I believe he enjoys doing missionary more because he is on the heavy side and he can control rhythm and how long it will last but I want to do more than just those two. I’m not really sure how to talk to him about it because I don’t want him to think his size is a problem I love him the way he is but I would like us to become more adventurous. Any one here gone through the same thing and what did you do to switch it up?