I see you edited your post. But here is what you do: forget about actual chastity hardware because that may scare off a girlfriend in the initial stage of a relationship. Instead, ease into it slowly.
For instance, do some role playing during sex where your gf is the dominate one, and you are submissive. When you are ready to cum, ask for her permission since "she is in charge." People like power, and she may tell you to wait a day, or longer.
You'll notice that the longer you wait between orgasms, the more attentive you'll be to your gf. For instance, you may offer her more back rubs than usual, or perform oral more often, etc. She'll quickly realize that there is a correlation between your attentiveness, and your lack or orgasms. So she will indeed control your orgasms.
Once you go 1-2 weeks between orgasms, you'll go crazy and get hard-ons throughout the day, and that will make you want your gf even more, and be even more attentive to her "needs." Since you want to be chastised, you'll adjust immediately because that is what you are after. And you'll relish the moments of "wanting" your gf.
And there you have it: chastity without the hardware. Of course, you must not masturbate because that defeats the whole purpose of chastity (unless she knowing grants you permission to do so).