Ban is inevitable, just a matter of when.
TBH you might be better off keeping what you got for a few more years and just going electric once the market has stabilised.
Banning diesel outright like Bristol has is very daft. What comes out the back of a Euro 6 diesel is exceptionally low at 0.17g/km for HC + NOx and 0.005g/km for particulates (28x less!). These really are minuscule amounts. A 20 year old bus guffs out clouds of black crap, is it
really any better environmentally?
The ban would be far far more effective if it was based on cars that were made in significantly outdated Euro emissions standards. For example a 1996 would be a Euro 1 emissions diesel, allowed 0.97g/km for NC+NOx and 0.14g/km for particulates. The petrol limits are barely any better.
I hope that councils around the UK have enough to brain power to realise this. As an Engineer, I really feel they have missed the point on this one.
Back on topic, I would buy a 2015 Diesel for the OP's mileage. It will have high pressure injectors, dual mass flywheel etc. and a dreaded PDF, but it won't have the silly adblu tank that was introduced ~2015 for Euro 6 emissions.
Or just go for a standard petrol turbo. There won't be a huge amount in it running cost wise.
One year ago my mileage dropped from ~22k to ~8k. I don't need nor want a diesel, but for me a main car is always best the devil you know.