If I were to provide a suggestion, I would start with fresh grinding your coffee from beans. You can get a pretty cheap manual grinder for like $20-30. I don’t remember the name of mine (it’s generic) but it was like $30 on Amazon and is great when I travel.
Next time you’re in a coffee shop, grab their cheapest blend. Coffee shops, in my experience, have fresher beans than the grocery store, especially if they roast their own coffee.
It doesn’t have to be the $26 organic single origin, just something that’s been roasted more recently than 6 months ago. Maybe you’ll be able to convince your S/O to get some better coffee in the future.
Another commenter suggested cold brew. That’s probably the best to maximize sweetness. Good luck!