You can certainly swap your run-flat tyres for normal ones (and doing so would be a good thing for comfort), but a space-saver spare wheel will eat into luggage space. The best way around this is to buy a tyre-repair kit - they're not ideal, but are better than nothing if you get a puncture. As for tyres, we've no experience of the M240i on different tyre combinations ourselves, but we've heard good things about Michelin Pilot Super Sports.