We also love to write emails during the day, it's amazing how you can get so carried away and sometimes end up writing an essay sex story. So emojis are great for this, I would suggest maybe look at some sexy vector art which sounds weird but you can get some really clean illustrations to add to your emails and message sessions.
Another suggestion would be to search for "intimacy" & "love making" rather than anything explicit as this is usually really toned down but still quite erotic. You can always try sending Gifs too! I don't really know any specific websites but google images, tumblr and other image based social sites are great for this sort of thing. You can also find sexting emoji dictionaries online which show a list of emojis you can string together ha