Should I use multivariate testing for checkout optimization?

I've been running my Shopify store for two years now, and conversion optimization feels like a constant battle. Our checkout process has always been a bit of a mystery—we get decent traffic, but something always seems to break down when customers are about to complete their purchase. I've heard about multivariate testing, but I'm honestly overwhelmed. How many variations should I test? What metrics matter most? And more importantly, will the effort of setting up complex tests actually translate to meaningful revenue gains? My team keeps pushing me to be more data-driven, but I'm worried about spending weeks on testing and seeing minimal impact. Our current checkout conversion sits around 35%, which I know is leaving serious money on the table. I want a systematic approach that doesn't require a PhD in statistics or weeks of development time. My biggest fear is investing time and resources into testing that doesn't move the needle, or worse, accidentally creating a more confusing checkout experience that drives customers away. I need a practical, no-nonsense strategy that can help me understand exactly what's preventing customers from completing their purchases.