Suggested New Rules (or House Rules) based on things that came up during play...
1) Option to use Dexterity for Climb rolls if in light armour and unencumbered
2) Option to have spellcasting in 5 feet of an active enemy to require a Wisdom roll to Concentrate or don't cast spell or use slot
3) Option to have bows and crossbows in 5 feet of an active enemy require a Wisdom roll to Concentrate or don't manage to get a shot off
4) Option to give Disadvantage if shooting through friend or enemies
5) Option for a combatant to give themselves disadvantage ( only if they don't already have it ) in order to enter a "stance" where they get Opportunity Attacks from any enemy movement within their melee range, not just from movement away. Alternatively to be able to Ready an attack with disadvantage, triggered by attempted enemy movement that prevents movement if it hits.