Why do you feel it particularly has to be a diesel? Unless you're doing considerable mileage (ie probably 15k or more) in a year theres practically no point in buying one and the DPF issues in newer ones would compound the issue even more so at low mileage. What sort of miles do you intend to do and how much do you have to spend?

The Nissan Note is worth a look: if that's too small try the Toyota Verso or Mazda 5.

I'd agree that a petrol engine is a better bet unless you do more than 15,000 miles a year. The reaon for that is that dlesels cost more if you're buying new, and if you're buying secondhand they are more liable to expensive failures.