Managing 4-5 wholesale vendors at once without losing track of margins, how do you do it?

Location: US
MOQ: Depends on vendor, usually a few hundred dollars opening order
Proof: Running a mid-size ecommerce store doing around $10k-$50k/month

Running a mid-size online store selling general merchandise and I've gotten to the point where I'm pulling inventory from 4 or 5 different sources at a time. Keeping track of which products came from where, what the actual landed cost was after shipping, and whether the margin I calculated at purchase is holding up after fees has gotten messy.

I'm currently working with a couple of Kole Imports wholesale vendors among others. They're one of my steadier US-based sources, good variety and domestic shipping, which at least helps with the math on landed cost. But across all my suppliers I'm still running everything in a spreadsheet and it's starting to break down.

Anyone using a specific tool or software to manage cost per unit across multiple vendors? I looked at Inventory Planner and a few others but nothing clicked yet. Would appreciate hearing what's actually working for stores doing $10k to $50k a month.