We use Peter Pig's rules - Square Bashing - but that uses lots of figures, generally mounted 3 to a base, 4 bases to a unit. Lots of units per player (divisional level?).
You can use Peter Pig WWII rules (PBI) instead, a company level game, still uses 3 figures per base, generally 6-8 bases per unit (each unit is a platoon), only a few units per player, usually just 3 or 4.
There used to be a starter extract of PBI available free to download, only gave the basic infantry rules, basic weaponry, no vehicles etc, but that's not an issue if you use them for 1918 instead of 1939.