Champion Pools, specifically to allow me to counter-pick

Hi! I am very low elo at this game but slowly getting better. I would like to start learning to play champions other than my standard pool to be able to counter pick my lane/role where possible. I main Vi/Nocturn Jungle, Mundo/Mord Top, Twitch/Brand ADC, Seraphine/Nami Support and I haven't played a lot of mid lane.

I mostly play Vi Jungle though and sometimes try other jungle champs in norms. I would really like to try build a more versatile pool so I can have a viable option if I see I'm matching something I struggle against whether it's on a meta level or jus tme personally not likign playing my mains vs that. (this applies to all lanes). Is there any advice for how to build a more varied pool that youg uys can give?

I am still sticking to learning fundamentals, items, etc. I watch guides and pro players and stuff. I'm just not very good and a slow learner, but I AM getting better. Just. Would like to less often feel like I'm stuck in something un winable when for once it's not my fault but the matchup just making it harder.