As someone who's experienced this from both sides, I'm Versitile and so is my BF. We're both above average sized, me 7.5 long and 6.5 around, him 8.5 long and 5.5 around. The best course of action is lots of a good lube and preparation getting yourself loose enough by using fingers starting with just one then adding another at a time until you get up to 3. Once you can take 3 fingers comfortably then you should be able to take your partner, for that session, you may have to do this each time you bottom. Most guys aren't as thick as 3 fingers so you should be fine. The main thing is lube and keep relaxed.