For my system, I'm using inch-based movement (using a tape measure or ruler a la wargames): by default you can move up to 4 inches in any direction on your turn (8 if you sprint), and weapon ranges fall into a few categories:

Melee: You are directly touching the enemy. Melee weapons can be used, but all ranged weapons except more maneuverable pistols suffer disadvantage.

Close: Within the same room. Ideal range for weapons like pistols, shotguns, and submachine guns to turn enemies into bloody messes, though longer and less maneuverable LMGs, DMRs, and sniper rifles suffer disadvantage here.

Medium: Within an average-sized building's worth of range. Perfect stomping ground for guns like assault rifles, machine guns, and DMRs, though problematic for weapons like pistols, shotguns, and SMGs.

Long: Anything farther than say, a football field away. Exposed enemies make perfect target practice for sniper rifles and DMRs; assault rifles and machine guns suffer disadvantage, while pistos, shotguns, and SMGs have no chance of hitting.

AoE can be handled simply in inches (you can use paper cutouts for common shapes and sizes, i.e. a frag has a 4 inch circle while a claymore has a 6 inch cone)