I would say the things which are most prominent in my mind about having sex in the position you mention are:

1) The weight of my partner on top of me. I love the feeling of being pressed into the bed by the weight of my lover - it's both a comforting feeling (like a big hug) and I think there are also power and control issues which make it feel good.

2) The sensation of his pubic bone against mine, puts pressure on my clitoris and, again, his weight adds to that pressure, added to which the feeling of him in my vagina gives me a more satisfying sensation than any other sensation I can have during sex (even if I don't reach orgasm).

3) When he thrusts into me fast, it does make my breasts bounce, and I find that can be painful, but it's one of those pleasure/pain things which all adds to the moment. I love that he enjoys watching them move while he's inside me and the feeling of my breasts being exposed and kind of vulnerable can be a turn on. I love it when he sucks on my nipples when we're in this position as it turns us both on.

I think those are the main points, but it really is almost impossible to describe - I find the missionary position to be one of the most fulfilling both physically and emotionally, so it's hard for me to describe in physical terms without the emotional aspects of the experience creeping in.

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