The only premium cock ring I can think of that may give an advantage over what your already using is the Lelo rings but their very expensive for what they are.
So I think your best bet is to get a vibrator. Why not look at the various massager's available as their not intimidating, can be used for sensual massages yet will allow her to experience the vibrations of a full on sex toy. The hitachi magic wand and super silicone massager were both great but have been discontinued however a variety of other massagers are available.
A simple bullet vibe is a good place to start, they're small and unintimidating but can really pack a punch with the strength of the vibes. I can personally recommend this little beauty: http://www.lovehoney.co.uk/product.cfm?p=10157
I haven't tried it personally, but it looks fun with its 2 vibes and the option to pull the lower ring over your balls aswell, or to let it hang down infront of them etc etc.
I wonder whether your wife is a little intimidated by vibrators - I was back when my only knowledge of them was all the huge rabbits in Ann Summers. It might be worth looking at something less "vibratorey" like the little clit vibes they do on here.
It's a bit marmite; some love it, some hate it but it's something you can incorporate into sex (you can enter her while she has this in) which sounds more like what you were interested in.