Death House will require heavy editing to be survivable by a single 1st level PC. Even for a party of five it’s a meat grinder. That’s actually part of what prompted me to write The Beast of Graenseskov (link in sig); I felt there should be a more story-focused low-level introduction into Curse of Strahd that wasn’t so deadly & offered ways to “win” without necessarily resorting to combat.
That said, I think you could play up the haunted aspects, maybe borrowing from Pathfinder’s haunt rules & creating a list of tasks to accomplish in Death House to end the haunt. The one thing I’d absolutely get rid of or drastically change is the shambling mound (IIRC) in the basement; I’ve seen and heard many parties dying there.
So we finished Death House this past weekend. And my GF decided to fight the Shambling Mound despite my most horrific and dangerous description of it. She did not feel like retreating was an option. And here's the thing...she beat it. But only just BARELY.
Honestly I was SHOCKED. So for reference here was the scenario. As special rules I provided higher than normal stats, so she had that going for her. I also stated that she would get Max HP at each level. But she was only a level 2 Druid, so that's still 20 HP. The DMPC was a Paladin 1 / Celestial Warlock 1 (with Polearm Mastery). So between the Bear attacks, Polearm Attacks, and Hellish Rebukes, they did a crapton of damage. Eventually they fell back (Disengaged) and since they moved better than Mound they got 1 round of ranged attacks. My GF used one Healing Word to get the DMPC back in the fight after she was knocked out (GF was knocked out of Bear form prior to this).
Now, behind the DM screen...I did not pull any punches, but I did separate them. I attacked both targets instead of focusing one. But I did not fudge any dice rolls until the very end. The round order was Jax (Druid), Shambling Mound, Aerith (Paladin/Warlock). One crit by the mound knocked Jax out of Bear form, but she had another use. Jax also got a lucky crit early on and did about 30 damage in one round. Aerith got very lucky and managed to land both Polearm hits consistently. The only thing I fudged was at the end. The Mound was down to 12 HP and I rolled...x2 20's, critting both players. Jax had 2 HP and Aerith had 6. Technically that's a TPK, but for as close as they were to defeating it and as close as they were to defeat...and the fact that there was only 2 of them, I called it a pair of misses. Aerith was able to do 14 damage during her turn. I debated on fudging that roll and let Jax get the final hit, but it was a literal 50/50 for her to hit it with her Scimitar, and the killer DM in me couldn't fudge 2 rounds in a row with the Mound.
But I was still super impressed that they did as good as they did. Moon Druids are no joke (and we all know Polearm Mastery was stupid good). Although they did BARELY make it out of the House. Jax was a little more nimble and got out, but Aerith took too much damage on the last Scythe Trap and fell (Jax was able to stabalize). So I was ok with those 2 sitting in the middle of the street with no resources, no HP, and barely having escape Death House. =)