For my fellow high handicappers, what was the #1 tip or tweak that helped fix your slice?

I am a high-20s handicapper, I've always played a few rounds of golf here and there over the years, but have never wanted to actually try and get better until a few months ago. Been playing at least 1 round a week for a few months now (more recently it has been 2 or more rounds a week). I've seen my game improve drastically just from course exposure and developing some mental cues, however, the one thing that I can't seem to fix is my God-awful slice.

I've watched plenty of online tutorials and 18-birdies coaching videos (lol) and it seems no matter what I do, I can't seem to eliminate the slice from my tee-shots. Iron or wood off the fairway? No big deal, might chunk or skull it, but almost never a slice- if anything, I'm more prone to hooking fairway shots.

Tired of losing balls. For anyone who started off with a similar problem, I'm just curious what was the biggest thing to eliminate or at least have control of your slice? Thanks!

EDIT: I would also accept cheap ball recommendations so, at the least, it doesn't sting quite as bad when I send a tee-shot into the woods.