We've tried doggy style (one of my personal faves) and what my friend calls the "Four square," which essentially is him upright and me on my back. We've scissored, and mirrored, and spooned, and frankly we've contorted ourselves into some crazy stuff. I've ridden him and he's pounded into me, but perhaps that is more personal then you want to hear. My main point is that when you are writing and coming up with sexual positions keep in mind what actually WORKS.
Some positions really are really not about comfort (yes I have dangled almost completely off the bed upside down before) and are supposedly more about the "angle of trajectory." (Though that one made me feel like I was going to pass out and wasn't great enough angle to try again!) Some things are physically impossible without props like slings, balls, or wedges.
When you write about sex in some cases its great to throw in a position that will make your reader go "WO! I wanna try that!" but in many cases its more important to emotionally connect with the characters - if they're loving this particular position then you won't need to go into the actual specifics of how tab a goes into slot b. You can loosely describe and the reader will insert the rest. Don't spend all your time driving home the point about this kinky position your brain made up unless it is something important to the story (and a sweet little virginal girl and boy who are experiencing their first time aren't typically going to try an upside down and backwards flip.)