Migrate Web App to Multi-Tenant SaaS

We're a UK accountancy firm with a working internal practice-management web app (Cloudflare Pages/Workers, currently a key-value store). We want to move it onto a proper relational database (Postgres or similar) and make it multi-tenant, so we can license it to other firms as a SaaS. Auth and billing to follow. Milestones: 1. A small paid trial task first, so we can assess fit. 2. Migrate the data model onto a proper database, on a copy of the system. 3. Multi-tenant structure (one shared database, clean tenant separation), then customer sign-in and billing. Important: all trial and early work is done on a copy with sample/dummy data - no access to our live system or real client data. We handle regulated data, so tenant separation and security matter. You: experience taking apps to multi-tenant SaaS and Postgres migrations; Cloudflare a plus; comfortable working to a written brief; UK/GDPR-aware preferred. To apply: briefly describe one similar migration you've done, and how you'd approach the trial task. Fixed-price milestones preferred.