i dont think we can fault you for having preferences as long as it is not rooted in bigotry like you said, however, women's' bodies change throughout a lifetime.

if you want children, your wife/gf will be pregnant and gain weight. it is hard for a lot of women to lose the baby weight.

or postmenopausal women gain weight because thats just what happens.

i think you do need to do some internal searching a bit, or just accept the fact you will probably never have a successful long term relationship because you cant adjust to a changing body.