I know this is a silly question but I'm genuinely stumped. Searching for it online has brought me to a few shady websites but nothing that appears to be legitimate. Can anyone point me in the right direction?

I'm not looking for level WADs but quality of life things like
being able to freely aim/look on screen,
change the game resolution,
increase my FOV,
customize all controls,
and so on.

I've found zdoom.org (and I'm still going through it) but I know there is more out there. I just don't know where to look.

http://dengine.net/

So you're not looking for mods, you're looking for advanced source ports with more features.

If you already know about ZDoom, then you can take a look at -- same engine, but with OpenGL rendering, so you can look all the way up and down instead of having to contend with the limits of [url=http://zdoom.org/wiki/Y-shearing]Y-shearing.

You can also look at the broader list here.

Mods/WADs/PK3s: Doomworld or the ZDoom forums are usually the best places to start, but there's always small pockets of cool things elsewhere because Doom modding's just that popular. Also check the sticky. I wouldn't really bother much with ModDB, they're almost all in those places already. I guess Brutal Doom's more popular there, but that's mostly because it's the most well-known one.

Sourceports (IE what you're looking for):
ZDoom
GZDoom
PRBoom
Chocolate Doom

At this point just about everywhere Doom is you'll either find sourceport or WAD talk.

As someone else mentioned, Doomworld is a good resource for WADs; the front page has all kinds of new stuff, but the 'levels' link on the side should take you to their archives.