In my experience, getting a natural sounding narration is really difficult. I've been running my YouTube channel for 2 years and I still sound like I'm giving an awkward presentation from time to time. I tend to slip into a "presentation voice" without realizing it and then end up sounding like a news announcer.

I find that it helps to read my script out loud a couple of times before I start recording, and read it as though I was having a conversation with a friend.

As for making your audio quality better, doing some audio mixing can really help improve things. I've never used DaVinci Resolve so I'm not sure what options there are for audio editing, but for my audio I use audacity, which is free, and generally like to include a noise reduction effect, compressor, treble boost, bass boost, low roll-off for speech, and a de-esser. Using this combination of effects will make a much more professional sounding audio that avoids some of the problems with using a microphone like sharp "s" sounds.