Jousting is treated as a bonus action which does not cost the player anything, and does not strictly require making a melee attack. In order to joust, you must be 1) riding while wielding a lance, and 2) move in the same direction twice in a row with an enemy lined up at the end of the 2nd move. When this happens, the enemy is attacked automatically.

When riding, a lance will count for much less weight than it will normally, because your saddle is presumed to have its own stirrup for the lance. When wielding the lance, it reverts to its full weight.

Rename the lance skill to “jousting”, and make lances not count as polearms for the purpose of applying them at range.

Lances go through one or two levels of visible damage (e.g. “cracked lance”) before being destroyed completely, rather than being able to break outright. Repairing the lance with the same methods being used to repair erosion will fix this damage, and erosionproofing it will make it immune to cracking or breaking.

Centaurs can use lances as if they were riding.