Shields just giving a +2 can be boring. Here’s what I found as an alternative for a little bit more modular shielding for your characters. The base requirement for using a shield is having shield proficiency.
Buckler: +1AC, but is light enough to strap to your forearm so it doesn’t take up a hand. Cannot equip weapons in this hand. Costs 10g
Kite Shield: +2AC. 12 strength requirement. Costs 15g
Tower Shield: +3AC. 16 strength requirement. Can spend an action to plant the shield, freeing up the users hand and providing a stationary 3/4 cover. Takes 1 bonus action to remove from the ground and 1 action to reequip. Lowers speed by 5ft for each size smaller than large. Costs 60g
The buckler is more useful for a caster to have a free hand to cast spells that have somatic components without resorting to a feat. The kite shield is your usual shield. The tower shield is still work in progress. I’m thinking of reducing the action economy burden of deployment and reequipping to “attacks” rather than actions, just like you can shove and attack if you have multiattack.