If you were silver 3 last season and haven't improved you're probably around silver 4 skill since skill level at a given MMR/ELO tends to go up over time due to players getting better and either forcing others to get better or pushing previously higher players down by replacing them as they get better and move up.
More to the point, the champs with the most ability to mess up and still be useful are utility and tank champs, so support type stuff like
or
or
.
You don't like those champs (or are bad at using their utility so you become useless to the team), so what you're looking for are low mechanics requirement assassins. Avoid champs like
and
like the plague as their mechanics will be too much for you and the fact that their kit is balanced around how strong they are if played RIGHT means they will be weak for you if you're making mistakes.
You want to find champs like
,
,
,
, and
since they have a lot of point and click abilities that may be weaker than skill shots, but are harder to mess up so overall they will be stronger for you.
Also consider
since he brings burst which you might like, but also brings utility to the team and helps out everyone, while also being pretty tanky when he has his feast stacks up so if you mess up a bit there is a bit more safety. Hope that helps and good luck getting back to silver. The climb is pretty easy and it's a fun trip :D