Brembo

Hi everyone 😬, will be purchasing a used BMW with in the next couple of weeks and want help making a decision. ideally I want something reliable as I’m in the process of buying a house and won’t have lots to spend afterwards. I'm looking for ether a 1 series or 2 series with a max budget of £15k, what engine would you guys recommend and what sort of mileage are those engines good for ? Have mainly been looking at the diesels but not a massive fan of 3 cylinders engines 116d/216d etc Also is BMW approved used what it’s cracked up to be ? ( this is the only place I’m looking atm ) Also the only extra that I want is the Harmen Kardon audio upgrade, haven’t experienced it but is it a big upgrade over the standard sound system ? really appreciate any help on the subject. I thought the best place to ask would be here 🙂 thanks in advanced 👍🏼