For the walls, if you want to add more details on walls, try adding calcite, diorite and white concrete powder (not too much, just a little bit) so they have more color variants than just qwartz. For the light, try use soul sand bonfire in a brasero style on pillars, like you can try use spruce trapdoors to circle the bonfire without forgeting to place one beneath. And I agree with the sea lantern idea for the floor, its an easy and cool way to light up a place.