After the whole Irene episode, Sherlock starts reconsidering his views about sex. He never had the will or time before but now he is curious about it, maybe starts touching himself and is ready to finally lose his virginity.
Irene isn't around anymore. Of course he could go for a professional but he prefers someone he knows: Molly Hooper.

He explains her that it's stricly sexual and she accepts even if of course she would like more but that's better than nothing. And she is quite flattered to be his first.

So I'd like to see !Virgin Sherlock / Molly.
With shy, anxious, lost Sherlock and Molly being super tender, loving and a very patient teacher.

The first times are a bit akward but then it gets better and Sherlock is a quick learner.
Up to you if it turns or not into a relationship.

Bonus if Molly accidentaly gets pregnant.