BigCommerce Upsell and BNPL Improvements

My BigCommerce store is stable and already generating sales, but it needs a visual refresh and smarter upsell functionality to reach the next level. I want conversion-focused on every screen size.

Alongside the new look, I also need full-stack support for:

• Upselling and optimized checkout flows that surface add-ons, cross-sells, and post-purchase offers without slowing the site down. Especially, buy now pay later promoting/marketing.
• Graphic assets that match the updated design (icons, banners, and any custom illustrations).
• Coding the redesign directly into BigCommerce (Stencil, HTML/CSS, JavaScript) and keeping performance tight.
• Ongoing long-term edits, so any future tweaks or A/B experiments are handled quickly.
• Integration with third-party services—think email marketing, reviews, or shipping apps—using BigCommerce APIs or ready-made apps when they make sense.

Deliverables will be considered complete once the checkout upsell logic works end-to-end, third-party integrations sync correctly, and Lighthouse scores remain in a healthy range.