Car manufacturers went through a period of making electric folding hard-top roofs increasingly complicated, meaning they can get problematic when they get old. I'd be looking for something with a fabric roof. A Mazda MX-5 is a good choice with a very simple roof but only has two seats and limited boot space, so it may not be practical enough for your needs. You can get soft-top versions of the Citroen C1 and Peugeot 108, which are very affordable little city cars, but they're not really 'proper' convertibles. An Audi A3 Cabriolet is a good mix of style and practicality, as is the MINI Convertible.