Thanks for the help in the previous thread, a lot of good stuff was posted there!
I wasn't able to try all the mods yet, but I had some problems in a few mods recommended, they were designed for expert Doom players, something which I'm not. :P
Can anyone tell me about mods where the difficulty is close to vanilla Doom I, II?

Sure thing :)

Dammit soldier, this is a hell invasion, not a school fun day. Grab that chainsaw and get slicing till they are all gone...

All that matters is having fun.
Your definition of fun, isn't the same as mine.
People have different tastes, that's a good thing.
The world would be too boring, otherwise!

Of the wads I listed, Doom The Way Id Did (https://www.doomworld.com/vb/thread/58100) is more or less an attempt at creating a full set of levels very much in the style of the classic Doom levels as Id made them. For me, it feels like it's something Id could have done if they had had a year or three of additional experience in Doom mapping. So, somewhat cooler looking and more polished levels, with better flow, maybe just a wee tiny bit more difficult. Definitely easy enough that if you've played the originals, these levels shouldn't prove to be too hard. Definitely not designed for expert Doom players.

Give it a try; it's a really nice wad especially for anyone who likes the original levels.

Doom 2 The Way Id Did is similar but for the Doom 2 levels. Which are harder than Doom 1. I can't say I like that wad quite as much, but then again, I can't say I like the original Doom 2 levels as much as I like Doom 1 levels. So I guess the mappers succeeded at replicating that part as well ^_^; Again I feel compelled to point out that strafing isn't a Brutal Doom feature. You could strafe in the original Doom. And damn well near every source port makes it easy to set up wasd (or whatever) movement if it's not there by default.

Have you tried combining different mods?

Chillax maps - extremely hard.
Chillax + Brutal Doom + Unlimited ammo - extremely hard extremely fun.
Chillax + Russian Overkill - extremely fun.

I still recommend DoomZ map on top of my list. Something like R16 (release 16, I think). The later ones became confusing to me. Chop trees, build protection for night against zombie waves, fight dragons.. its very original. =)

I can't remember whether I knew back then that Doom had strafing, or mouse support for that matter. Strafing + directional keys is a bit tricky. Wish I knew though: it would've made the game a whole lot easier. Duke3D too in fact, which I guess must have been the last fps I played with directional keys only.