"A long haired big boobed girl who would dote on me?"
Isn't that Yunyun? Or alternatively, Darkness when she's not being crazy. Kazuma did like the way Darkness looked the most when he first met her, before he found out what her personality was like.
I honestly don't think that he'd be satisfied with Megumin's body in the long run unless she went through a growth spurt. Honestly, unless he picks multiple girls (or at least 2) I'm not sure Kazuma could be satisfied unless he narrowed down his criteria to his absolute essentials / favorites.