League of Legends (LoL) Question: I would like to main Support. What champions should I focus on?

Leona would probably fit your play-style. Leona is pretty similar to Thresh, Alistar, Braum and Blitz as they're all aggressive melee (bar Thresh) tanky supports and so you'll probably pick her up quite easily. She's very tanky and has a lot of CC, and has good damage during early game.

Squisher but still aggressive choices are Annie, Vel'Koz and Morgana. These are AP supports that focus on burst and poke. They all have good CC and deal a lot of damage but lack in defence, something you'll have to get adjusted to considering you seem to only play tanks atm.

Still squishy but not as aggressive as your current picks are Janna and Nami. Janna and Nami focus on poke and sustain as they're ranged and Janna has a shield and Nami a heal. They also both have a lot of CC, good peel and good engage/disengage. They're a lot squishier than the things you're used to playing, so it'll take some getting used to, but these two are both very good supports atm, especially Janna.

I would actually say to just look at your adc and adapt to that.

For example, you probably don't want to take an agressive support when laning with a Vayne due to her being a bit weak in early laning phases and much more oriented to the late game.
Except when your know your adc and you can communicate or the adc wants to play it aggresive. In that case, I would recommend something like bliz or thresh due to the pulls close to walls for a dubble stun combo.

When laning with for example a caitlyn, it would be wise to actually go with an agressive support or a support like Janna who can boost your ad and can shield you when you're making mistakes.

I would recommend just to pick out 1 or 2 champions from each category and play them according to your adc.

As example:
Aggressive burst (strong burst adc like Graves): Annie/Morgana
Aggressive tanky (adc's with slows & more constant dmg): Leona/Thresh/Blitz
Defensive (lategame/passive adc's): Janna/Sona/Soraka

I recommend playing Leona. She feels like a low-elo destroyer, granted they don't pick Morg (you *******s). And Morg is another interesting one. They're pretty simple in what their kits are but you can branch out after using them. Morg can help you learn about mage supports like Nami, Janna, Lulu, etc. and Leona teaches you about Braum, Nautilus, and other tanky supports.

I main support, but I'm Silver V so it's possible I might be incorrect. Enjoy supporting. :)

Try to play good synergy supports,
Leona, works good with champions like graves but is a bit off meta now
Nami, Always good
Janna, for early safety
Lulu, for early safety and hard matchups
thresh, you can still pick it vs a morgana botlane just be more patient with your q's
Morgana Always good but you need to be reactive
Zyra is good for teamfights and alot of dmg while still being able to peel

wow main Support is pretty cool. I think u have to focus on Nami, Thresh, Nautilus and maybe Janna or Lulu at the Moment :))

Leona for sure. Also try and get an adc-main friend to duo with you because soloq support is about as fun as soraka mid

A few supports I'd recommend are Leona, Taric & Morgana.
Leona has powerful engage and massive CC, she is quite easy to play and has high room for improvement. Her damage is high but a lot of people don't know when it's best to engage with her.
Taric has insane aura's for the team and thus benefits a lot in team fights, he goes best with high burst champions with good poke. Being slightly hard to play effectively with huge room for improvement. I would recommend this champion over the others if you have communication with your ADC (via voice software)
Morgana is a team fight / all-in support, since she has high CC early on she is quite easy to play but once you get your ultimate it can be quite hard to use her perfectly in team fights. She benefits most with a skill shot champion to make best use of her snare.

Morgana was my first love in the realm of supports. She is tanky and her binding spell helps secure a kill for the ADC. Sona is also great because of a well-rounded kit. She has good poke, heal, speed boost, and one of the best Ults in the game. Janna is pretty good too, but she takes a little more practice. If you wanna go for a kill lane, Vel'Koz is certainly a strong pick, but you might steal a few kills. For a slightly different (and tanky) pick, I like to support with Dr. Mundo. You can continually use his Q to poke, and by mid game you should already be too much to handle. For the aggressive, Volibear is awesome. Your sustain is outstanding, and that flip...I mean, who wants to get the Voli-flip? Good luck, summoner!