Fairlight/Freesound.org for professional indie audio mixing - impossible or achievable?

Hey everyone,

I'm Priya, a working Colorist, and I'm currently cutting my teeth on an indie short. We shot it on a C70 with a lot of natural light, using a LS 300x for fill, and honestly, the visuals are looking pretty slick. However, sound is proving to be a real beast. We had a boom op with an MKH 50 into a 833, but our locations weren't always ideal, and we definitely can't afford a pro sound mixer for the post-production stage.

I've been trying to tackle the audio myself in DaVinci Resolve's Fairlight page, and I've also been exploring Freesound.org for sound effects and ambiences to fill out some gaps. But honestly, getting everything to sit right and sound 'professional' feels like an uphill battle. It's difficult to get the levels and EQ correct, and the whole thing just sounds... amateur, next to our fairly polished visuals.

For those of you who've successfully blended these free tools to create a genuinely good-sounding mix on a shoestring budget, what's been your workflow? Is there a secret sauce I'm missing here?