Well, it depends on what “graphic mods” means to you…
Are you asking for tilesets, as in images that represent monsters, structures and items?
Or are you looking for the overmap graphics mod, that replaces the typical text-based map of the game with images?
Or is it something else?
To use tilesets, you need to download the “Tiles” version of the game, in case you have the “Curses” one.
As for tilesets themself; there are many (well, not that many, but still) and different people have different tastes… Do you look for something “realistic”, “comic-like”, “simple”, …?
Then there are also isometric ones…
A bunch of them come preinstalled in the base game, so you could just go through them all and see if something fits your taste.
The default one, called UltiCa, looks quite nice in my opinion - and while it does take up some RAM, it shouldn’t be that bad.
I used to stick to the ChestHole tileset, but it’s a bit outdated and more and more monsters are missing tiles (and are therefore replaced with letters).
Some might recommend the UnDeadPeopleTileset, but since it’s no longer in the base game after… “the incident”, it’s a hassle to keep it up to date. And I noticed that it eats up a bit more resources too, but still; even old computer/laptops should be able to run it “fine”.
I might remember it wrongly, but the game launcher should come with some tilesets to choose from, including the UnDeadPeople one.
As for the overmap graphics mod, this also comes with the game and can be activated as a mod when creating a world.
There are some special installation instructions in the readme of the mod.
I don’t see any problems at all for running this mod on a laptop (or older computer in general).