The issue for women/mouth is the girth/length size of you verses the size of her mouth and how much she can take. I have a small mouth and a pronounced gag reflex so can't deep-throat, but have never had complaints about what I CAN do.
As for penetration and girth, I know wider hips can usually take more depth and girth, but in virtually every case, proper preparation beforehand with lots of stimulation and lubrication plus patience from the guy is key to success. If there's enough oral/finger/tongue stimulation *before* you try penetration, the woman will be so stimulated and ready for you.
My first husband was 9" by 7" and he *always* did a lot of slow preparation and made sure I had a great orgasm before he tried penetrating me, so by the time I was screaming in ecstacy, I was pulling him into me, begging for it. If you spend time patiently preparing her, she'll not only tolerate your penetration, she'll love it and give you sex anytime you want, because she'll know you put her needs ahead of your own, which will also make her far more relaxed and eager. Sex starts in the brain and should flow from the heart.
My two cents.