>>1290 (OP)
I can advise you the following stretches and exercises for sexual awesomeness:
Exercises for sexual competence
Planking, rotisserie rolls, other core-area workouts - this will help you last when on top of her, core stamina is important for missionary or any sex position where you're on top of her.
Squats, lunges - Sex is mostly hips and leg action, with arms as a means of support.
Cardio - For stamina in general.
Stretches for sexual competence
Most of these are yoga poses, so it should help you enough.
Horse Pose, Child's pose, deep squats - Keep that pelvic-floor nice and loose so you can come like a beast.
Cobra pose, king cobra pose, bed-hanging - Keeps your core loose, because missionary.
Bridge pose, downward dog oise, butterfly pose (wall) - keep the legs nice and loose too, they support your hips, which hold your baby-making center.