2015 216d Active Tourer (sunroof model) + roof box?

Hi everyone,

I"m about to buy my first ever BMW and I have a few questions I'm hoping you can answer.

For context I'm buying this as it's a bit of a treat over other options in my price range and I'm not ready to go for a full on 4x4 (too expensive) or an estate type car (too long).

I have three children so I needed something with a bit of space but I'm worried this will not quite do and that I'm choosing form over function. To help with this I'm curious is anyone has one of these (with the large sun roof) and also a roof box that fits to provide extra space for the once a year family trip?

The version I'm getting doesn't have those bars that you normally attache a roof box to and I can't seem to find a good solution through my searches. I'm hoping I'm just missing something and that there is a way to get a roof box onto one of these with the sunroof.

Any advice or alternative solutions would be much appreciated as I really like this car.