Get a shapton 1000 grit ceramic whetstone, they're excellent and not terribly expensive.
Those 4 sided ones are neat and all, but a decent stone will give you a better edge especially if you combine it with stropping.
I hate to suggest r*ddit, but r/sharpening was pretty good
Get a honing steel if you don't already have one to help maintain the edge as you use the blade too, I keep one in the kitchen.
YouTube would probably be another place with good sharpening tutorials but you really just need a stone or two, an old leather belt to use as a strop, some stropping paste, and a honing steel. Shouldn't cost more than $50-60 total.
The stones eventually wear down of course, but they'll last a good while and you can flatten them when they start to dish.