...don't add huge landmasses or buildings to the game? I don't mind objects and NPCs, but something that greatly changes everything isn't something I want. Don't want to put too much load on my computer.

Been browsing the Nexus but it seems most of the popular ones add way too much for me.

Ayleid Steps doesn't add giant landmasses, or anything that changes the look of the map, but it does add a bunch of new dungeons. House Valranis adds NPCs, and tucks a couple buildings into different corners, but they don't look out of place. David Brasher's Fighters Guild and Mages Guild quests also don't add any new buildings or landmasses that I've seen. New NPCs, and some new things, but in existing areas.

Those are the most low-impact ones I can think of.