well quinn can be a flex pick for top,jungle,mid, and adc if needed
ekko can flex top and mid
yorick can flex top,jungle
octobitch can only top and dont have alot of great match ups currently
kat is ok mid , i personally thing ahri is all around a better champ
as PohPe suggested i am a fan of top lane hard cc /tank champs like mao,malph but in the current meta mao is a bit nerfed and not as dominate (mao top main) swain can play top and does well (super sleeper op right now) viktor is always viable mid (currently) and he just out scales most champs
but if you want another flex pick i would pick up galio ... for top/jungle an i have played him mid and support as well...
so other champs to consider
considering their flexability in what lane they can play
but the more champs you know and learn the better cuz of the knowledge you gain and would know how to play against them when facing them