My first thought is, you’ve got to check out Archive of Our Own. The tagging system is honestly a lifesaver. Filter for the pairing 'Son Goku/Chi-Chi,' then apply the 'Explicit' rating filter. A lot of writers there put real care into the emotional build-up, not just the, well, lemon part. Sometimes you'll find stories that explore their married life dynamics in ways the anime glossed over, which adds a layer of depth that makes the explicit scenes hit different.
Another spot is FanFiction.net, but the search is clunkier. You sort of have to wade through a lot of other 'Dragon Ball' content. A pro-tip: using the community filter for 'lemons' or searching 'G/Chi' in the summaries can narrow it down. The writing quality varies wildly, from super cringey to surprisingly tender. I’ve stumbled across a few hidden gems that way, but it feels more like a treasure hunt compared to AO3's curated feel.
Honestly, sometimes the best stuff isn’t even labeled 'lemon.' I found one story focusing on them rebuilding their relationship after the Cell Saga that had a single, incredibly well-written intimate scene that felt way more earned than most dedicated smut. So, maybe don’t filter too aggressively. The old-school DBZ forums are pretty much dead for this, though. I miss the wild west days of individual Geocities sites, but the convenience of modern archives wins out.