How are you tracking which acquisition channels actually convert to paid?

We're about 18 months into our SaaS journey with ~$15k MRR and I feel like we're flying blind when it comes to attribution. We know signups are coming in but have no idea which blog posts, Reddit threads, Product Hunt, or LinkedIn posts are actually driving conversions to paid. We tried UTM params but we lose them by the time someone signs up two weeks later. GA4 is a mess to interpret. Anyone built something solid for this? Looking for something founder-friendly, not another enterprise analytics platform that takes 3 months to implement. Currently losing sleep over this — feels like we're spending on channels that don't work and ignoring ones that do.