You've seen a lot more dramas than I have, but I was able to find a few not on your list:
1. One Spring Night (leads have to keep their distance from each other because FL has long-term boyfriend)
2. My Mister: Sexual tension, but one-sided. This drama is worth watching anyway. It is amazing.
3. Unfamiliar Family: Leads are BFFs and don't want to risk that.
4. Marriage Contract: Leads start out as having fake marriage and when feelings develop don't know how to transition out of that. Somewhat similar to Because It Was Our First Life, which is on your already-watched list.
5. I Don"t Love You Yet: Extreme BFFs who adore each other but both think the other doesn't want a love relationship. This one is kind of frustrating to watch, lol.
This category interests me as well, so I would be interested in any recommendations you have. :)
Edit: I just noticed your favorite actress is IU. How could you not have watched My Mister yet? :)