I will admit that I actually felt the want to breastfeed my own grandchild in this way. She was well-fed (breast in this case) by my daughter and there were no problems but it was something I definitely felt. I was postmenopausal at the time.
I hope I haven't offended anyone but I thought it important enough to mention and I am not promoting breastfeeding or grannyfeeding.
I also have always had modest boobs but breastfed three children. I don't think it matters whether you are big or small as my daughter has very large ones and managed it. I will ask her about the latching on part.