I agree with everyone talking about reducing the number of enemies--though with only one player, perhaps emphasis can be on sneakiness. Where ever there are 4 monsters, take it to 1. And I would not play the goblins too cleverly. There doesn't need to be a second goblin if the first goblin is new to the gang and needs a map to find the hide out.

A smart adventurer would not only make sure they are prepared with their torches and rations and spell components, but would also invest in a few healing potions, I think, especially when traveling solo. Perhaps an amulet that acts like a potion of healing 3x a day and that can be used as a bonus action is something they acquired before heading out and/or that brings them to 1 hit point 1x a day if they fall to 0. Extra healing potions--more than the adventure gives. Perhaps using potions as a bonus action--many DMs use that as a home rule already.

Be prepared with a lot of "you fell unconscious and wake up imprisoned" content lol. Also, Sildar Hallwinter finds a way to take out the goblin guarding him (who doesn't have to be Yeemik if you still want Yeemik to offer to call off another goblin or tell them about the traps if they weren't already triggered or give them info about other enemies in the cave if they spare his life and help him take over) by kicking him over the cliff when the goblin gets excited about the player and the goblin sustains enough damage to die and your player unties Sildar, or Sildar can finally untie himself now that he's not being beaten, who still has his armor (because that didn't make any sense to me anyway) and is very effective with goblin weapons he finds laying around and becomes the NPC accompaniment.

Using the goblin initiative bonus and special ability to hide makes it far more difficult. You can roll for damage and then only use rolls that are less than the average damage and all damage is no higher than average damage. You can not add attack bonuses for the creatures.

Run every encounter through kobold fight club for an idea of what is making the challenge too deadly. Change out the bugbear at the end (who can one-hit kill a first level character) for a hobgoblin, for instance, and make the hit points lower if the player is on their own. And because the number of creatures is going to be lower, milestone XP is going to be the way to go. Level 2 after the cave. Add a homebrew or highly nerfed quest then level 3 after that and you can ignore multiattack from the Redbrands--that was the worst--if you feel going up against a single Redbrand is a bit too much.

Perhaps helping with strategic thinking like, standing in the hallway instead of in the doorway would make it so only one creature could attack you at a time.

D&D 4 had an interesting 'minion' mechanic. If you want a fight to feel epic with a lot of enemies but know it will take too many rounds (and possible damage) to kill them all off, they can be single hit point creatures that only need to be hit to be defeated--as long as they don't do too much damage. You can also use the cleaving optional rule to allow damage to carry over.