Sloane Square to Gatwick

You want to be at Gatwick by 0830.

Sloane Square to Victoria is one stop on the Underground, then train Victoria To Gatwick, but take a taxi if you want

I think depart soon after 0700.

Pre-book assistance with Southern Rail at Victoria Station- https://www.southernrailway.com/travel-information/travel-help/assisted-travel

They will then contact Gatwick station as they will then know what train you are on and Gatwick station will provide assistance into the terminal.

Since you have mobility issues, my suggestion is to pre-book a car service. They will pick you up at your hotel and drop you off at your terminal.

A car service is a flat fee and probably much less than a taxi..

but Gatwick is a bear by car from central London. Slow busy roads, no motorway until the last bit.

And rush hour and school run traffic into the mix.

I’d go with Isn31c’s plan, especially booking assistance - I’ve nearly missed a flight taking a car to Gatwick, the traffic can be terrible.

Thank you for your responses. An early start and Gatwick express sounds like the plan

An ordinary Southern Rail train is a better option than the Express. The latter is considerably more expensive and only 2/3 minutes quicker.