So its a Q5 quattro 2.0litre tdi Yes? This has a gross weight(ie max allowable weight of fully loaded car)of 2365kg for 6speed & 2430kg for 7speed As you passed your driving test after 1997 then you will have only a B licence limiting you to combined max gross weight of both car & caravan to below 3.5tonnes.
So you need to choose a caravan with a max gross weight(mtplm)of no more than 1135kg for 6speed or 1070kg for 7speed. these are well within car max tow limit.
Max gross weight of car & max gross weight of caravan(known as mtplm)added together must not exceed 3.5tonnes to allow you to drive it on licence you have. Remember these are max allowable weights not actual weights of car & caravan which might be somewhat less than 3.5tonnes.
Your car is capable of towing a larger caravan, up to about 1500kg mtplm keeping within 85% ratio recommended for safe towing but to tow this you will need to pass another test to give you the required B+E licence.
1170 is probably the biggest also. If the figures in ROG's link above are correct then a higher spec car may only leave you with a caravan with a gross laden weight of 970kg.
You will be looking at smaller and more basic caravans.
If you want a heavier van you need a lighter car, or take your towing test.
It depends how you want to do your caravanning. Keeping within your existing B licence you can get a UK built new small 2 berth or you could get a much older & larger lightweight 'van like ABI Marauder in reasonable nick for less than £1000, usually about a tonne all up but probably not what you want.
There no longer seems to be a market for new lightweight basic caravans although foreign makes like Sterckeman might be worth a look.
If you want a much larger new caravan then you need to take test to gain E licence to give you B+E. If you do this then you could get a caravan of around 1500kg mtplm or even larger than that & keep within towing limit for your car although 1500kg would give you the 85% ratio recommended but it is not a legal requirement.