You could just have a really good review of all your finances to minimise your expenses. MSE will walk you through this:
Do a money makeover and potentially save £1,000s - Money Saving Expert
Then set up standing orders to separate your money into different accounts, eg:
One for shared regular bills
One for shared monthly essentials, eg food, petrol/fares
Savings for your surgery. If you're not quite at the 'need to remortgage' stage, you could work out what your mortgage would cost at current rates and start to live now as if that's what it costs and this will help start saving towards your surgery
One for shared annual and irregular expenses eg insurance, car repairs, Christmas etc
An emergency fund/large purchases fund (any home improvements, car repairs etc)
After all the above, and any other essentials/agreed joint costs, split the rest into the personal spending accounts. Don't touch any of the accounts other than the food etc account and the personal spending accounts and you use these on a 'when it's gone, it's gone' basis'.
Achieves the same result as YNAB for free and once it's set up, it just runs itself, except maybe check once a month that everything is working as it should. Any account that you're accumulating money in should earn interest - either set up linked savings accounts or use Kroo/Starling etc which pay interest on a current account.