This is a really common situation and I think you just need to go in ready to accept whatever answer he’s going to give you. You have to decided what is more important to you as a person and then base your own decision off that.
But as to how to approach him just bring it up gently. Sit down and tell him you’re interested in something a little different. I would sit down and make a list of all the things that you’re interested in so you can have them right there with you and you can talk it over with him and figure out what is completely out of the question and what you’re both willing to try. He may surprise you!
The strongest thing I can stress is don’t push it. If he’s not interested in something then pushing it is going to damage your relationship in the long run. And men’s ego’s are very sensitive things. Make sure you don’t make it sound like he isn’t satisfying you.
Suggest small things like maybe you lay out his clothes for him every day or give him a back massage once a week. Start little weekly ritual’s that don’t neccisarly demand alot out of each other. Test the waters and then you can make a more complex schedual. I think the biggest thing is to remember not to just dive in and go in all at once. Ease yourselves into it. Learn together and find out what each of you likes and wants. Even if it doesn’t work out in a D/s way you should use this exploration to come closer to one another and fall in love even deeper.
Im sorry if this answer isn’t what you are looking for. I am writing this and barely able to keep my eyes open. If there is a specific issue I didn’t address please feel free to ask!