First off I would avoid mechanically difficult champions when you play ranked. So instead of taking say Jayce, Riven, or Yasuo top, take Ryze or Maoki. Right out of the gate you are already better off in lane because Ryze or Mao is much easier to play mechanically so you can more easily split your focus to watching minimap for example, to better avoid ganks. Less room for mechanical mess ups less room for bad stuff to happen in lane. Those are also champs that better help set up ganks for your jungler.
This applies to bot lane as well. Avoid Thresh or Nami generally speaking. Much easier to get the same general effect with Leona and Sona and they are much easier to play. Seems those were champs you were already using anyway so shouldnt be an issue for you.
I would try amumu over sejuani. He is a stronger jungler and especially if you have flash up his ult is near impossible to miss. If he gets banned or taken you can always fall back on sej. Malphite might be a better fallback though as he has a simpler less likely to miss ult to use and he is generally tankier. One of my own personal weaknesses is mechanics so I have found it very helpful to avoid mechanically difficult champions in favor of ones that are harder to mess up for climbing ranked.
As too supporting focus less on trusting or not trusting your ADC and instead start trying to read them. Do they get to lane and start harassing the enemy at the expense of farm? If their harass works, make sure you dive as soon as you hit 2-3 with Leona or try to mirror their aggressiveness with sona so its hard for enemy to trade back to your ADC. Does instead the ADC just farm and seem to have no interest in harassing? Then play more passive an focus on keeping them safe. When the enemy adc moves up to CS feint forward like you are going to attack to see if they back off and miss the CS. But don't dive because you already know your ADC's priorities are farming. Save your dive for if your jungler shows up to gank. This will make for a boring lane but its better than forcing your ADC to take fights they dont seem to be looking for.
Also keep in mind the issue of sustain. If you are playing sona and the enemy lane has no heals you can afford to trade more just make sure to pause in between trades to heal up.
One thing I noticed when I looked at your profile, match history, etc is that your rune options are pretty limited. I main support as well and I have several different pages depending on which support I am using and how I expect the lane to go. For example when I play Sona into a high burst lane like vs a leona or thresh, I run a very buiser heavy rune page. I run armor reds and quints, heal seals, and scaling mr glyphs.
The Leona's then dive me expecting me to blow up but instead I can eat their engage well and dish out damage in return. Within no time I and my ADC are healed up with W and now Leona or her ADC injured generally are afraid to re-engage. If instead I am facing a vayne while playing Sona I will switch out the armor reds for magic pen so I can harass vayne harder and bully her out of lane, especially if she doesnt have a heal support.
So in short, play the mechanically simple champions, have a couple for every role. The more uncomfortable a role you are put in the more safe and passive you should play so even if you lose lane, you dont feed so hard that you make it impossible for your team to carry you. Get a few more rune pages and supp champs so you can adapt to the matchups. If you are against a draven/leona and your adc is immobile like Ashe or Varus, playing Taric over Sona will make sure you survive the laning phase. Just save your stun for when leona dives your carry and stun their adc. Plus the heal keeps your ADC safe to farm.
And as always wards, wards, wards. This is especially usefu when you are NOT supporting as it will be a huge boost to get an extra ward or two from you each back considering at your elo's i imagine there is not much warding.
Those are some of the strategies I used to get to Gold mostly supporting.
, for some of them you won't have trouble mashing buttons..
