How sweet of you! Many individuals enjoy vibrating dildos and even double dildos during pegging sessions.
There are plenty of us, however, who love doing it without the extra stimulation. For me, I love the energetics and the visuals. Knowing that a man is relaxing enough to take a cock, and watching him (his face, his body) respond to my strokes is almost overwhelming in and of itself. And the wave motion of my own body as I concentrate on connecting my pelvis to his is hypnotic and can induce its own calm sense of ecstasy.
Not to short you on what you are looking for however - there are many great vibrating dildos on the market.
Vixen is my hands-down favorite dildo producer. They use the highest quality silicone (which they title VixSkin) and their products come with a lifetime guarantee. I've been eyeing the Vixen "Mistress" dildo myself.
Its six inches long and 1-1/4 thick. Could be a little big for a beginner - but not necessarily with a nice long lead up full of rimming and delicious, delicate finger massage around your tight yet yielding sphincter. At the least, you'd be able to get the tip in.
Happy perving!
xoxox
Tori
PS
Tantus is another high quality dildo producer, just for good measure.