Looking for advice on car insurance

My boyfriend and I are coming traveling in Europe in about a week, and are looking to buy a camper van to explore Europe.

We have found someone who is willing to sell his van to us in Koln, but he is unable to tell us more about obtaining car insurance as a tourist.
From what I've learned so far, is that we need to get third party liability insurance and "green card" insurance to drive around Europe. Can anyone tell me if this is all possible to get as a tourist, and if you need any other kind of insurance to be on the save side?
If anyone knows of a good insurance company to contact (that speaks English), that would help us out greatly!

Please let us know any information you might be able to share with us!

Thanks in advance for all the help!
Cheers,
Melissa