You don't actually need AoO to play a sword-and-board protector type and keep the squishies safe. All you really need is a rule that says that if you want to stop someone from moving past you to get to someone behind you, you can force them to engage with you instead of whoever you're protecting. No free attacks, just a "if you want the little guy you're going to have to go through me" sort of rule.
This was how we basically played when we played BECMI back before 3e. It didn't have AoO rules except for the "if you try to disengage from the battle, your opponents get a free swipe at you as you run" rule, but there was a tacit understanding that the fighters and clerics were standing between the monsters and the thieves/wizards at the back of the party, and if you wanted to attack them in melee you'd have to go through their protectors. (With missile combat and sneaking up from behind tactics of course being different stories). And of course my monsters were the same, with a front line of orcs or whatnot protecting their spellcasters and/or archers from the party's frontline. We'd limit it to two opponents you could stop - if your opposition was large enough that they could tie down your front line at two apiece and still have more to spare, your squishes were going to get squashed. (I could see upping that to maybe 3 these days, or making it higher for high level games, but back then we didn't think that way - two seemed reasonable so we went with it).
When you play on a tactical map with grids and such you can get a lot of "well what about if I do this" sort of thing to try to get around that kind of protection, so AoO rules help clarify things. But if you're not playing the tactical map version of the game they aren't strictly necessary - either in theater of the mind or the more loose "here's a diagram of what's going on" without a grid - so long as you keep in mind the intent behind them.
This was how we basically played when we played BECMI back before 3e. It didn't have AoO rules except for the "if you try to disengage from the battle, your opponents get a free swipe at you as you run" rule, but there was a tacit understanding that the fighters and clerics were standing between the monsters and the thieves/wizards at the back of the party, and if you wanted to attack them in melee you'd have to go through their protectors. (With missile combat and sneaking up from behind tactics of course being different stories). And of course my monsters were the same, with a front line of orcs or whatnot protecting their spellcasters and/or archers from the party's frontline. We'd limit it to two opponents you could stop - if your opposition was large enough that they could tie down your front line at two apiece and still have more to spare, your squishes were going to get squashed. (I could see upping that to maybe 3 these days, or making it higher for high level games, but back then we didn't think that way - two seemed reasonable so we went with it).
When you play on a tactical map with grids and such you can get a lot of "well what about if I do this" sort of thing to try to get around that kind of protection, so AoO rules help clarify things. But if you're not playing the tactical map version of the game they aren't strictly necessary - either in theater of the mind or the more loose "here's a diagram of what's going on" without a grid - so long as you keep in mind the intent behind them.
