Definitely missionary with her legs up and the pillow underneath.
The deepest penetration position is with her on her side and you staddling her, with her lower leg lying between your legs. You will find that your hips do not get in each other’s way and you will sink it to the bone. No joke.
This is really, really nice if you can’t quite bottom out on her. You’ll love the feeling. But if you are long enough you will smash her cervix, so be careful. I am not sure you can get under a cervix in that position (unless your dick is significantly curved to the side).
I’d avoid woman on top - she could get too aggressive and drop you out of her.
-BH