Looking for....

I've alredy read most of Abe Miyuki and Yamamoto Kotetsuko's works. And also Silver Diamond

I have to say, I can think of several excellent ones that are on the longish side, but less than 20 chapters. That said:

http://www.mangago.zone/read-manga/dog_style/ -complete
http://www.mangago.zone/read-manga/the_summit/ -incomplete and likely to remain so
http://www.mangago.zone/read-manga/under_grand_hotel/ -complete
http://www.mangago.zone/read-manga/sakura_gari/ -complete (very long chapters, so putting it)
http://www.mangago.zone/read-manga/hidamari_ga_kikoeru/ -ongoing, currently at 19
http://www.mangago.zone/read-manga/katekyo/ -complete
http://www.mangago.zone/read-manga/ameiro_paradox/ -ongoing, more than 20 only if counting extras
http://www.mangago.zone/read-manga/hidoku_shinaide/ -ongoing
http://www.mangago.zone/read-manga/elektel_delusion/ -complete
http://www.mangago.zone/read-manga/heart_no_kakurega/ -ongoing, more than 20 only if counting extras
http://www.mangago.zone/read-manga/hinekure_chaser/ -ongoing
http://www.mangago.zone/read-manga/love_stage/ -complete, but last couple aren't on here
http://www.mangago.zone/read-manga/aitsu_no_daihonmei/ -ongoing, but not being updated on here
http://www.mangago.zone/read-manga/19_days/ -ongoing
http://www.mangago.zone/read-manga/blood_bank/ -complete
http://www.mangago.zone/read-manga/kijima_kun/ -ongoing
http://www.mangago.zone/read-manga/warehouse/ -ongoing
http://www.mangago.zone/read-manga/never_understand/ -complete
http://www.mangago.zone/read-manga/geu_kkeute_issneun_geos/ -ongoing

And a heads up, some of these are pretty fluffy, but a few are quite dark, some tragic

Wow that's a lot! Your kindness is so much appreciated. Thank you very muchh!!

You're very welcome.