Question about getting my wife into wanting to cuckold me

Ive been secretly wanting to watch my wife get fucked by another guy for awhile, while we were having sex today I was unable to make her cum and thought it would be a good way to introduce the idea of it. I started by saying “too bad my dick isn’t bigger, and then I’d be able to make you cum more” and she played into it saying that she bets so and that I need to somehow enhance/ enlarge my size. I told her I don’t really think that’s possible (I’m only 4 inches), so I told her “or we get someone with a bigger dick than me for you” and she originally turned it down then I said “you never know someone with a bigger dick might be able to make you cum a lot more than me” she then kind of changed her expression (this was all while we were having sex) and she then said that she was just concerned with making me cum right now so I told her that’s what she always does and that we need to focus on making her cum more.

Does anyone have any advise on how they got into doing this? And next steps I should do to keep popping the idea in her head?