The side-by-side position is better if you interlace your legs rather than have her one leg under you. One of the reasons is that she is going to wake up in the morning with a dead leg. The other reason is that where the gal has to bring her knees up for you to achieve further entry, it normally ends up with having her leg just under your floating rib. If you can fall asleep with her knee against your ribs, fine.
I'd recommend to the bros here the spoon position, is much better for slow sex and falling asleep together type. Of course, I'd also use the side-by-side position, but with our legs interlaced.
I've never tried the wheelbarrow or frog and the advanced rear entry i think is better known to me, or rather the gals as reverse cow girl.
With the missionary, if you can, put a pillow just under the small of her back. This elevates the vagina thus enabling you to go for a deep entry.
This is from my experience with my gers, may differ for other bros, go ahead and experiment.
