Struggling with Cold conversion/gain damage/best spirit gem for Sorceress.

Hey everyone,

I like to start with blind runs and try not to follow builds. I'll grab a few ideas here and there but I'm still having issues with understanding conversion.

For a while I was using Elemental Conflux and Archmage, while using Blueflame Goldcast gloves and Brotherhood ring to- so I thought at least, convert the Fire and Lightning back to Cold to maximize my Cold Damage buffs. Apparently that does not happen in POE2.

So now I'm wondering this- is it worth keeping the two mentioned persistent buffs if my initial damage is enough to justify the gain of other elements? Or is there a better persistent buff I should look at?

Lastly, does "Gain % of damage as extra cold damage" itself then get increased by my damage modifiers?

Ex: 100 cold damage increases by 300% to 400 damage

Gain 50% as extra cold damage: 200 additional cold damage

Does the extra 200 then get increased by 300% also? I'm so confused.

I know I'm asking multiple questions so any help would be appreciated to any of the topics above.

Level 91, having to play T15 maps cautiously but clearing well enough. If I raise boss difficulty to max, they take 2-3 minutes and I risk dying. If only level 3 boss, they melt.

Survivability seems well enough, I only die if I don't kill something fast enough. 1590hp/4990es max resist and 46% "armor" from ascendancy. 2h staff plus focus, level 27 skills.

I have not fought any citadel or pinnacle bosses yet or ever before. Has me worried.. thanks again!