I have watched many of these types, and they are usually great. I'm looking for more, hopefully somebody can help.

Coffee Prince is most famous, then I like Arsenal Military Academy, also My Unicorn Girl. IMO those are very strong in what I'm looking for.

The main theme is the FL is cross-dressing, and it's a very strong thing throughout the drama, not just the occasional dress-up because she's going to the market, but it's a important aspect of the character.

And also romance with the ML.

But it doesn't have to be cross-dressing, a tomboy aspect is good too, like Secret Garden, FL is very tomboyish there.

A decent number of Thai dramas have that theme if you don't mind the usual Thai drama tropes:

Leh Game Rak

Pachara Montra

And two non-Thai ones that come to mind:

Shine or Go Crazy

The Heiress

"To The Beautiful You" is a good one if you haven't seen it already!

The Kings Affection 

Thanks :D will take a look at those I haven't noticed before.

I'm actually watching When You Be Me   and it fits my criteria perfectly, and in a way I didn't think of.

It's a "soul swapping" drama, so ML and FL swap souls. But the female (now occupied by him) turns into this total tomboy with an attitude, because that's what the guy was before the soul swapping, while the girl was a total shy nobody. It's a interesting soul-swapping drama and keeps me watching.

So more like that as well :)

Coffee prince (classic kdrama!!)
Love in the moonlight (historical drama)