Print-On-Demand Specialist for Children's Books

I’m looking for an experienced print-on-demand consultant to help me choose the best POD service and plan the setup for two personalized children’s books that will be sold through my own website (via API integration).
• Book A: ~34 pages, full color, ages 3–6
• Book B: ~120 pages, mostly B&W with 25 color pages, ages 7–12
• Both books are personalized, meaning the child’s name and some images/illustrations will change based on the customer’s input.

I’m currently considering Bookvault, but I’ve heard mixed reviews. I need help evaluating Bookvault, Lulu Direct, IngramSpark, Blurb, Gelato, Cloudprinter, Peecho, and other suitable POD options — focusing on print cost, quality, API capability, reliability, and revenue share.

What I need:
• POD comparison and recommendation (best + backup choice)
• Cost/margin model (including mixed color pricing for Book B)
• Advice on trim sizes, binding, paper, and color options
• Guidance on API or Shopify/WooCommerce integration for automated personalized orders
• File setup checklist (color specs, bleed, PDF/X standards)
• Short consultation session to answer a few final setup questions

Goal:
Find the most cost-effective, high-quality POD solution that supports color printing, dynamic personalization (text + images), API automation, and low platform fees.