Headroom might be an issue in some. In the 3.5Ts (assuming it will just be Clydie in there), you might want to look at the Renault Master based ones, since they are front wheel drive and therefore the floor can be a lot lower and that in turn can mean more headroom (think there are 2 height types, you would prob need the higher one).
Other than that it might be a 7.5T. Not sure of your 'vintage', does your licence allow you to drive over 3.5T (if you passed pre 97 it will do). If not you would need to do a towing test for it.
We recently downsized from a 7,5T to a 3.5T as the only traveller now is my 14.2 rather than my now retired 17 hander (hence the interest in head heights of lorries!)