If the towbar gives a maximum weight that is the maximum even if the vehicle is OK for more- it is the lowest figure in either case. I think you are making the right decision to get a trailer.
Have a look at the Dave Cooper folding trailer. http://www.davecooper.co.uk/trailers/trailers-for-bikes That is a good item if you are short for space. Dave does some other basic trailers at a reasonable cost as well. I would strongly advise you to avoid the mistake of buying a secondhand trailer off eBay or similar. Very few people sell up for any reason other than the trailer is worn out. By the time you have replaced the wheel bearings, tyres and lights you will have spent more than a new item.
The other option is a goods trailer and the extra faff of strapping the bike into the cargo box. In my opinion it's worth getting a wheel bracket for the front wheel if you go that route, they are easy to fabricate or you can buy one ready made for purpose built trailers like the Franc. Most small goods trailers will store stood up on the tailgate to take up less space.
Don't forget your [legal] speed will be reduced when towing and you cannot use the outside lane on a motorway. Your van insurance should cover towing at no extra cost, just double check (some insurance companies consider a towbar as a "modification" and you need to tell them you have one fitted).