OK, I think I know what you mean here. You want to play the Dom. Sub roles, just not to the point of wearing leather masks and whips, chains and handcuffs stuff. Well it all kind of depends on your tastes and how far she is willing to take it. First thing first, you have to understand that this is all an illusion, all d&s stuff is. The illusion is that the dominant party is in control, when actually in all D&S play there is a code word when once said everything stops. That word is spoken by the submissive party when they have had enough, so actually they are in control since they can stop it whenever they want. It would be a good idea to discuss a code word.
It is hard to tell you anything about what you should plan with out letting us know what kind of stuff you both are into. We know that you like to watch her masturbate. OK, well have you thought about purchasing vibrators or a dildo? I know I know you probably don't want to be see going into the local sex shop or your wife won't go into one.
Here is a great site
http://www.distinctivetoys.net
They are very discreet and they won't contact you. It is run by Sue Johansen who has a sex show on sunday nights on the oxygen channel.
Give us some more info and we may be able to offer further suggestions.