As Lutz states, this is diffuclt with the paucity of information.
However, as your wife is disabled I would suggest you take a lot of time actually deciding what you want. You need to look at the type of van layout that will suit her, and your needs and then if a shortlist is made, then you look at what type of towcar you need to make it all work. Will the van need any modifications, and if so are they available to you etc? You mention a Mgane Scenic as a choice compared witha saloon car, but apart from greater headroom, I really cannot see that mcuh of a difference. If you were looking at a vehicle with a large rear sliding door access, then i could see the difference. Again, if your wife needs space for access then you need to look at vans that can allow this and have layout that does not clutter too much at the door.
I suggest visit one of the larger Shows and look at what is on offer and get a feel for the layout that may suit. If you plan to buy new than the manufacturer may be able to modify the van to better suit you, if it is 2nd hand then at least you have a choice of models and can get after sales work done, it required.
Don't forget that by the sounds of it, you will do all the manhandling yourself so a motor mover sounds a good idea possily in a smaller van, and that will take up payload..
Take your time, do your homework and talk to as many dealers as you can. All we can do is make suggestions as we have no idea of what you actually need.