I run a WordPress / WooCommerce store that sells printed phone-case designs. Each of my 300 products shows one fixed artwork; what needs to change is only the phone-model mockup laid on top when a customer picks their device from a dropdown (≈ 800 models). Here is exactly what I need built and tuned: • On every product page the design image stays locked as the background. • The dropdown swaps only the transparent PNG mockup that sits above that background—ideally via AJAX so the page never reloads. • The solution must scale smoothly to 300 × 800 combinations without slowing the site. • Any code should sit in a lightweight custom plugin or child-theme snippet, not a bloated page-builder add-on. Once the feature works, please tighten overall performance—compress and lazy-load the mockups, configure proper caching, and make sure Core Web Vitals stay green. I will supply all design backgrounds and phone-model PNGs; you wire up the front-end logic, back-end management interface (bulk upload or mapping table preferred), and any image-optimization settings. A short hand-off note or screen-share showing how to add new designs or models will complete the job.