How do I get my wife to go black and hung

Hi I'm mike I've been married to my wife gem for 10 years this October .shes 36 and I'm 38
Every time we make love I always feel that I'm not big enough for her in the trouser dept but my oral skills are second to none
So I never leave her un orgasmed
But wen it comes to ** her deep I can't seem to go deep enough
On the odd occasion whilst we've had a load of alcohol she's always said she really craves trying a BBC
So after my ** twitching so much and ozzing pre ** we're both agreeing that trying this would be a great idea for her to feel a real big ** stretching her and going deep.
I have said to her that we could always find a hung blk guy on the web and she agrees
The problem is the next day wen she has sobered up all ideas of last nights ** fantasies go cold
So how do I get her to acually go threw with this because wen I'm mentioning this BBC the night before her ** get extremely wet of the thought !
So I went out yesterday after a little information off the web to buy her a big blk ** so hopefully she could get used to the idea of seing a blk ** stretching her **
Please help with any advice on this situation as I clearly know she wants it