For my wife it would be with me sitting with my back against the headboard with my legs spread and her sitting between my legs leaning back on my chest.
That way I can gently play with her nipples or rest my hand gently on hers as she masturbates. She really loves that.
She also likes me to be wearing nipple clamps so that as she squirms against me the clamps are being dragged backwards and forwards pulling at my nipples constantly.