Have you checked out the Wye and Usk Foundation? They have a number of stretches you can book. It's expensive (£20+ a day ticket) but you do tend to end up with quite a stretch to yourself. There are also really good catch reports online which can give you a lot of info on which areas of the stretch have produced in the past. As a visiting angler, I've found this a really useful resource. Sure you'll find them on google.
In terms of "below Ross", I've fished Wyatstone Leys, Wyebank, Courtfield, Middle Hill Court and Kerne Bridge and caught barbel from all of them.
Just one note though - how mobile is your old man? I only ask because some of the bank access can be pretty steep sided and not so easy for anyone with any kind of mobility issue. If that's any kind of concern, I'd be inclined to think about courtfield and fish the Legg Meadow area, as it's a relatively easy walk from the parking area and not to much mountain goat action is required. My own favourite swims on that stretch are in the wood section, but at this time of year it's definitely a good idea to take a rope with you to help you get in and out of the swims.
