Problem is we already have a map.
That’s why I propose to add “fog of war” which can be uncovered by any player.
Cartographer can howether write down areas he uncovered (whole map or the part he chose). Then if given to another player, he can open this map and update his. Our cartographers can add markers, notes, cities etc.
I don’t believe this idea is very hard to implement AND it will add exploration excitement.
As for something to write on - a vellum (calfskin) was used in those times I believe.