The biggest hurdle you have is that the traditional route to 'save money' by buying into a year old approved used car, with ongoing manufacturer warranty etc. and other 'new car' ease of running, just doesn't work at the moment.
Rather than making a massive saving due to initial depreciation, you're probably actually paying more for immediate availability.
I just looked up the 118i M Sport on BMW AUC and CarWow.
CarWow suggest new price is available at £26,000.
The cheapest 1 year old example on the AUC site is £23,500 with 16k on it, so only a £2,500 saving from what you could pay new. There's only 2 under £25,000.
Yep current used prices are a joke. Not sure if the increased costs are making their way to the customer with higher prices on your trade in?