Website Redesign & Responsiveness Upgrade

My current site is ready to publish but links and font size of design should be optimized. I need a front-end refresh that focuses on one clear priority: true responsive design. Every page must adapt smoothly to smartphones, tablets and desktops without breaking the existing content structure or branding. I want to add payment gateway also. You will take the files that are already live, rebuild the layout in clean HTML5 and CSS3—Bootstrap, Flexbox or another lightweight framework is fine—then hand back pages that scale fluidly, load quickly and pass common mobile-friendly tests. Please keep the navigation, colours and copy exactly as they are; the task is purely about presentation and fluid grids, not new features or re-writes. Deliverables: • Fully responsive versions of all current pages, tested on iOS & Android phones, popular tablets and the latest desktop browsers • Minified CSS/JS (if any) plus unminified source for future edits • A short read-me that explains folder structure and how to deploy the upgraded files on my host I’ll supply a ZIP of the existing site as soon as we start. Let me know roughly how long you’ll need and share one or two links to previous responsive work so I can see your approach in action.