Are you really a Londoner? There's a mahoosive NCP on Park Lane at the West End of Oxford St and numerous smaller car parks nearby, that you can pre-book on line to ensure a space, but most Londoners I know would rather eat a porcupine than drive across that part of town during the day, anyway, so its a bit moot.
Qualifying disabled Londoners can use Dial-a-Ride, and there's a lot of public transport into that part of town, including some step-free access via tube (admittedly not on all lines).
Honestly the main reason for the flight from Oxford Street and the surrounding area is that retail property and Business Rates are almost prohibitively expensive, which makes it difficult to justify keeping a branch open there. Up until the recent changes, John Lewis was paying £16.5 million a year, just in business rates, never mind rent, staff, security and cost of stock. That reduced to ~ £6.5 million rates per year in 2023., which is still a lot.