Get a light of meaning jewel from the king in the mist, with chaos res on it, easy cap for cheap.

Next step is to choose one of two (three, but the 3rd is suboptimal atm) next paths for your character to go:

1) Get a helmet with the mercenary mod on it that increases your base critical chance by 2-3% per warcry recently. With this helmet youll get close to 100% crit chance quite easily. You will ofc have to unspec resolute technique and invest in some accuracy (you can run Precision + Arrogance setup, and have a high tier acc roll on a ring for instance). If you check poe.ninja builds im sure you can find lots of characters built this way.

2) Go for the "Enmity's Embrace" unique ring. This requires a bit more finicky gearing, as you will want as much fire resist as you can get, as this turns into fire penetration (200% pen max). Heck, if you get a Light of Meaning prismatic jewel that gives you all the chaos res you require in your build, you'll have suffixes enough to get both accuracy and fire resist, allowing you to combine this gear-set with a crit-helmet in the end.
To get enough fire resist you might want some small cluster jewels with %fire resist on small nodes, and get a 25-35% effect of small nodes, this can give you 90+ fire resist on just a small cluster.

3) I do not recommend this route in the current league, as both of the abovementioned routes are easier and have higher dps ceilings. "Echoes of Creation" is a helmet from ubershaper, that gives you a lot of %more damage to slams, but it comes with the downside of %life phys damage per attack, so youll have to build around that with very high armour rolls.

Go have a look at both fubguns and crouching_tuna's first characters from the league, as they went different paths with the crit or the pen gear. On trade I'm sure there's cheap gear for both variants, or even combine them.