I'm not into wearing diapers so have never bought any, but she's open to it, 5'3" ~120 pounds, she wears small in everything, with a girlish figure, not much bigger in hips than waist.
If I don't get any input, I'll get the L/XL Girls Goodnites, but I'm worried those might be kind of big on her? Not worried about long term or heavy use, am worried about what would be cutest and most comfortable for her since it'll be her first time. I'd prefer a less bulky option. What about the biggest Underjams, or some other option I haven't thought of?
She's the first person I've told about my perversion for girls in diapers and she took it great, yay what an awesome girlfriend.