Taking things up a notch

I know there are a few similar posts in here already, but in looking for advice and would hate to overrun someone else's search for advice too, so...

When my partner and I originally got together, he really struggled to maintain his erection, and when he did he couldn't cum. We talked about it, and he explained that he was incredibly nervous about sleeping with me because he was worried that I'd freak out and end the relationship early on because of his 'interests'. We talked and discovered that our sexual preferences (?) were very similar. Now, further down the line, our sex has improved massively and we're comfortably settled into a very happy relationship.

The reason for my post today though is that I feel like we've kind of hit a wall. Don't get me wrong, I'm still very happy with him, but I want to take things up a notch - to experiment a little more now and to integrate more of our sexual relationship into our lifestyle in general - but I don't know how to bring this up...

I've always found it difficult to express my feelings about such things, and part of me feels that as he is the dominant partner in our relationship, it's not really my place to bring this up? So some advice...how can I broach this subject, or how can I hint to him so he'll come to that conclusion himself?

Thanks guys. I think I just needed some reassurance that this was something u could just bring up with him. I feel so comfortable to talk to him about anything usually, but it's like I can't get my words out when it comes to things like this.