As mentioned above the cheapest (and greenest!) option is to keep the current car going, especially as the secondhand market is hugely overpriced at the moment. According to webuyanycar my Dad’s A6 has gone up 30%+ in the last 6 months!
If you decide on another car then any big estate will meet your needs – Octavia, Superb, Passat, Leon, A6, 5 Series, V70, Subaru, Hyundai…. Or an S-max if you want huge space and the option of a couple of extra seats. They are all a muchness so find one that has the best mileage, engine, kit compromise for your budget. I had an XC60 and it was crap. Not very roomy, poor handling, unreliable (leaks like a sieve around the windscreen), uneconomical and the auto box was slow and annoying. My Passat has much more room and is better in every way. My old S-max was very practical and surprisingly ok to drive but I did have problems later from 50k miles onwards.