Boss Fight Action Economy

I love single-enemy boss fights or mini-bosses. I find them both easier to manage as a DM and more epic for the players (given the scenario is appropriate). I’m currently designing a campaign/mega-dungeon meant for levels 1-9 ish, and I’m wondering… even for low level characters, should I be giving a boss legendary actions to balance the fight such that it’s not a cakewalk for the players, without having to over-tune the damage or enemy CR?

For example, a CR 2 bandit captain is tough on their own, but against four or five level 1 players, the fight could end quickly. Should I give said captain 1 or 2 actions for an extra move or offhand attack? Thoughts?