I spent many middle school and high school summers 1:1 gaming, primarily in AD&D 2nd Edition. And more than a few sessions recently, in 5E. As a player, and as a DM.
As others have stated: utilize henchmen and hirelings. This is the classic "Jason and the Argonauts" model. Go watch Clash of the Titans and see if that turns your crank. I love it. As a player, I enjoy seeing to the well-being of my troops, equipping them, promoting or demoting them, making the tough decisions to send them into situations where some will surely die. As a DM, I love the easy leverage over the player. You can instantly and effectively dial up tension by killing a well-fleshed-out, named NPC. Just ask Corporal Dietrich and Private Frost.
Also: consider letting the player play two characters: a primary and a sidekick. This lets the player explore different class options and directly cover more bases (party roles).
Blend the two notions, and you get something like Disney's animated Robin Hood. The main PC is Robin, the sidekick PC is Little John, and the rest of the NPCs are the merry band. Or it's like the Gentleman Bastards: the main PC is Locke Lamora, the sidekick is Jean, the NPCs are the other Gentlemen.
Have fun! 1:1 gaming is a delight, because combat and decisions go much swifter. What you lose in interesting inter-party discussion you gain in plot momentum.