We had a similar job on my parents’ old cottage, where the doorway was slightly wonky and no standard door sat properly in the opening. They chose a bespoke timber design, and the difference was impressive once fitted, it looked original but closed far more securely. I’d ask about moisture-resistant timber, draught seals, finishing and whether the installer measures everything themselves. Doors Uxbridge may be worth contacting for ideas, but get a couple of detailed quotes before committing.
